Two exquisite new species of Hoplisoma (Siluriformes: Callichthyidae) from the rio Tapajós basin, Brazil, with a discussion on the morphology of the mesethmoid within CorydoradinaeAbstract
A crowdfunding initiative carried out by aquarists allowed us to sample tributaries of the rio Tapajós basin in the surroundings of Jacareacanga and Maués towns, Pará and Amazonas states, respectively, in the Brazilian Amazon. During this expedition, 13 Corydoradinae species were captured, from which at least five could be confirmed as new to science. In this article, we formally describe two of these species. Both new species can be distinguished from their congeners by having the following features: (I) ventral surface of trunk with small to relatively large coalescent platelets, forming a typical mosaic-like pattern, which entirely or almost entirely covers the ventral surface trunk; (II) small, whitish yellow or beige blotches at least on predorsal portion of body; and (III) a large, smoothly arched dark brown or black patch extending from anterior portion of parieto-supraoccipital towards region of interopercle, transversally crossing orbit and forming typical mask-like blotch. The new species differ, one from another, by the conspicuously different patterns of dark markings on flanks. Considering their peculiar head morphology, a broad discussion on the relation of the mesethmoid anatomy and snout shape within Corydoradinae is provided. Additionally, a discussion of the possible positive adaptive value of their color patterns is provided.
Keywords:
Amazon; Corydoras sp. “Ancestor”; Osteology; Snout morphology; Taxonomy
Resumo
Uma iniciativa de financiamento coletivo realizada por aquaristas nos permitiu amostrar tributários da bacia do rio Tapajós nos arredores das cidades de Jacareacanga e Maués, estados do Pará e Amazonas, respectivamente, na Amazônia brasileira. Durante esta expedição, 13 espécies de Corydoradinae foram capturadas, das quais pelo menos cinco puderam ser confirmadas como novas para a ciência. Neste artigo, descrevemos formalmente duas dessas espécies. Ambas espécies novas podem ser distinguidas de suas congêneres por apresentarem as seguintes características: (I) superfície ventral do tronco com placas coalescentes de tamanho pequeno a relativamente grande, formando um padrão típico em forma de mosaico, que cobre inteiramente ou quase inteiramente a superfície ventral do tronco; (II) pequenas manchas amarelo-esbranquiçadas ou bege pelo menos na porção pré-dorsal do corpo; e (III) uma grande mancha marrom-escura ou preta, suavemente arqueada, estendendo-se da porção anterior do parieto-supraoccipital em direção à região do interopérculo, cruzando transversalmente a órbita e formando uma mancha típica em forma de máscara. As novas espécies se diferenciam, uma da outra, pelos padrões de marcas escuras nos flancos conspicuamente diferentes. Considerando sua peculiar morfologia da cabeça, uma ampla discussão sobre a relação da anatomia do mesetmoide e o formato do focinho em Corydoradinae é fornecida. Além disso, uma discussão sobre o possível valor adaptativo positivo de seus padrões de colorido também é fornecida.
Palavras chave:
Amazônia; Corydoras sp. “Ancestor”; Morfologia do focinho; Osteologia; Taxonomia
INTRODUCTION
Callichthyidae is a Neotropical family of armored catfishes characterized by having two longitudinal series of dermal plates on the flanks (Reis, 1998, 2003). Currently, the family harbors more than 220 valid species (Fricke et al., 2024), of which more than 180 were, until recently, allocated in Corydoras Lacépède, 1803 (Tencatt et al., 2023a, b; 2024a,b), which made it one of the most species-rich genera of Siluriformes for decades. Even after the substantial efforts to elucidate both taxonomy (e.g., Eigenmann, Eigenmann, 1890; Ellis, 1913; Gosline, 1940; Nijssen, 1970; Nijssen, Isbrücker, 1967, 1980a, 1983, 1986) and phylogenetic relationships (e.g., Britto, 2003; Alexandrou et al., 2011; Marburger et al., 2018) of Corydoras, a series of issues in these fields remain unresolved (Britto et al., 2007; Tencatt, Ohara, 2016a).
One of the most notorious issues regarding Corydoradinae systematics refers to the paraphyly of Corydoras, which has been demonstrated over the past four decades based on both morphological (Reis, 1998; Britto, 2003) and molecular (Alexandrou et al., 2011; Marburger et al., 2018) evidence. In Britto (2003), the author proposed a classification to accommodate the major monophyletic groups recovered by him (146-148; fig.25). Although more recent phylogenetic hypotheses offer better resolutions for the interrelationships of Corydoradinae (i.e., Alexandrou et al., 2011; Marburger et al., 2018), including the non-monophyly of Corydoras as proposed in Britto (2003), the classification proposed by Britto (2003) continues to be used in subsequent works.
The phylogenetic study by Alexandrou et al. (2011) established nine lineages of species based on mitochondrial DNA, which were widely used in taxonomic papers as numerical “shortcuts” in many diagnoses of Corydorassensu lato (i.e., species within lineages 1, 4, 5, 6, 7, 8, and 9) (e.g., Tencatt et al., 2013, 2016, 2019, 2020, 2021, 2022a, 2023a,b, 2024a,b; Tencatt, Pavanelli, 2015; Tencatt, Britto, 2016; Tencatt, Evers, 2016; Tencatt, Ohara, 2016a,b; Bono et al., 2019; Bentley et al., 2021). Contrary to the remaining morphologically diagnosable clades (see Tencatt et al., 2023b:23), it was never possible to establish a morphological diagnosis between the species of lineages 6 and 9 (see Tencatt, Ohara, 2016b; Tencatt et al., 2022a, 2023b). The impossibility of diagnosing these clearly distinct lineages as presented by Alexandrou et al. (2011) was certainly the main reason for the imbroglio in resolving the paraphyly of Corydoras.
Contrary to the results of Alexandrou et al. (2011), more recent nuclear-based phylogenetic hypotheses by Marburger et al. (2018) (pyRAD) and Dias (2022) (Ultraconserved Elements) resulted in a topology similar to the one presented by Alexandrou et al. (2011), differing from it by recovering lineages 6 and 9 in a large monophyletic group. Considering this convergence of the results obtained by both data sources, a comprehensive study combining the phylogeny by Dias (2022) with the morphological data raised in the last two decades (see Britto, 2003; Tencatt, Pavanelli, 2015; Tencatt, Britto, 2016; Tencatt, Evers, 2016; Tencatt, Ohara, 2016a,b; Espíndola et al., 2018; Bono et al., 2019; Tencatt et al., 2019, 2020, 2021, 2022, 2023a,b, 2024a,b; Bentley et al., 2021) was performed, proposing a new classification for Corydoradinae (Dias et al., 2024). Considering the presence of available generic names for each of the morphologically diagnosable clade previously allocated in Corydoras, Dias et al. (2024) proposed the resurrection of four genera previously placed in the synonymy of Corydoras in order to reestablish the monophyly of the genus, namely: Brochis Cope, 1871, Gastrodermus Cope, 1878, Hoplisoma Swainson, 1838, and Osteogaster Cope, 1894.
With the new classification, Hoplisoma became the most species-rich genus within Corydoradinae, with nearly 90 valid species (Dias et al., 2024), which can be recognized by having the following features: (I) mesethmoid short in size, (II) posterior margin of both dorsal- and pectoral-fin spines typically with all or nearly all serrations directed towards the tip of the spine or perpendicularly directed, (III) posterior laminar expansion of infraorbital 2 ranging from strongly reduced to relatively well developed, typically not in contact with pterotic-extrascapular, (IV) single cranial fontanel, and (V) a combination of ground color of body pale yellow, brownish yellow or grayish yellow, typically with small dark spots at least in some part of the body and/or more than one large, dark blotch/stripe on body.
As widely discussed in previous articles, the appearance of putatively undescribed species of Corydoradinae in the aquarium trade is remarkable, especially from the rio Amazonas basin (see Tencatt et al., 2021, 2022a, 2023a, b, 2024a,b). Among the tributaries of the Amazon basin stands the rio Tapajós, which currently harbors six valid species of Hoplisoma, namely: H. apiaka (Espíndola, Spencer, Rocha & Britto, 2014), H. benattii (Espíndola, Tencatt, Pupo, Villa‐Verde & Britto, 2018), H. rikbaktsa (Lima & Britto, 2020), H. hypnos (Tencatt, Ohara, Sousa & Britto, 2022), H. thanatos (Tencatt, Ohara, Sousa & Britto, 2022), and H. psamathos (Tencatt, Ohara, Sousa & Britto, 2022), and 12 putatively undescribed species recognized in the aquarium trade by the following codes: Hoplisoma sp. C133, CW004, CW102, CW127, CW162, CW168, CW171, CW187, CW191, CW193, CW196, and CW203 (Tencatt et al., 2024a).
Considering the notably high number of Corydoradinae species in the rio Tapajós basin, especially in the regions of the Serra do Cachimbo and Jacareacanga town in Pará State, expeditions to these regions were funded by fish-keeping hobbyists from all around the world in crowdfunding initiatives. The first expedition, in 2019, mostly funded by the Research Assistance Program (RAP), an initiative created by Ian Fuller, founder of the “Corydoras World” website, resulted in the description of H. hypnos, H. thanatos, and H. psamathos, all from the rio Jamanxim basin, a tributary of the rio Tapajós (Tencatt et al., 2022a). With the aid of the renowned Corydoradinae breeder Eric Bodrock, All Oddball Aquatics and Greater Pittsburgh Aquarium Society, Inc. provided financial support to LFCT for a second expedition in 2023 to sample tributaries of the rio Tapajós basin in the region of Jacareacanga.
The expedition resulted in the capture of three Corydoradinae species, namely: Brochis bifasciata (Nijssen, 1972)(= CW135), Corydoras caramater Tencatt, Couto, Santos & Sousa, 2024(= CW83), Gastrodermus cf. pygmaeus (Knaack, 1966), plus 15 morphotypes recognized by the aquarium trades under the codes C151, C152, CW004, CW66, CW101, CW102, CW127, CW155, CW156, CW160, CW167, CW168, CW174, CW176 and CW193. Among the captured species stands one of the most intriguing species of Corydoradinae, Corydoras sp. CW004 or Corydoras sp. “Ancestor” (now Hoplisomasensu Dias et al., 2024), especially due to its peculiar color pattern, composed by a combination of: (I) dark mask-like blotch transversally crossing the orbit, (II) pale blotches on body, especially on its anterior half, and (III) dark blotches on flanks and some fins, especially dorsal and caudal fins, resulting in a unique color pattern within Corydoradinae.
Additionally, the morphological pattern of the specimens attributed to Hoplisoma sp. CW004 is also uncommon in the genus, especially regarding snout morphology, as raised by Grant (2019). The author recognized three different snout shapes in specimens assigned to CW004, with specimens with “rounder”, “straighter” and “straight, broad and wide” snouts. Based on Grant (2019), specimens with the “straighter” snout were recognized as non-conspecific with CW004, receiving the code CW155, while the ones with snout “straight, broad and wide” were coded as CW156. Subsequently, other specimens from the same region, but with slight differences in color pattern and head shape, were coded as CW167 and CW170. In tributaries of the rio Tapajós basin, Amazonas state in the region of Maués (neighboring Jacareacanga), specimens with a similar composition in color pattern were also found, but differing from the aforementioned coded morphotypes by having two longitudinal dark stripes on flanks instead of relatively small dark blotches. Also, similar variations in snout morphology were observed in these striped specimens, with each snout type being attributed to different genera by hobbyists and, consequently, receiving different codes in the aquarium trade. The specimens attributed to Brochis (then lineage 8 sensu Alexandrou et al. (2011)) were coded as CW160, whereas those assigned to Hoplisoma (then lineage 9) were CW168.
The analysis of specimens fitting both color and morphological patterns of CW004, CW155, CW156, CW160, CW167, and CW168 revealed the presence of two undescribed species of Hoplisoma, which are formally described herein. Considering the peculiar snout morphology of the new species, which resembles the pattern found in some species of Brochis, a discussion on the morphology of the snout within Corydoradinae is also provided, focusing on its general external aspect and on the anatomy of one of its main bones, the mesethmoid. In addition to discussing and providing insights into the characters available in the literature (i.e., Britto, 2003; Vera-Alcaraz, 2013), six characters and their putative character-states are raised here. Moreover, the possible positive adaptive value of the unusual color pattern of both new species is discussed.
MATERIAL AND METHODS
The generic placement of the two new species was based on the morphological diagnoses compiled in Dias et al. (2024). Measurements were obtained using digital calipers to the nearest tenth of millimeter. Morphometric and meristic data were taken following Tencatt et al. (2022b) and Reis (1997), respectively. Morphometrics are reported as percent of standard length (SL) or head length (HL). Terminology of barbels follows Britto, Lima (2003). Regarding the orientation of the serrations on the posterior margins of the dorsal and pectoral spines, terminology is according to Ballen, de Pinna (2021). For the osteological analysis, some specimens were cleared and stained (c&s) according to the protocol of Taylor, Van Dyke (1985). Due to fading of bone staining, some paratypes were re-stained in a solution of 75% ethyl alcohol and alizarin red S (Springer, Johnson, 2000) after dissection. Osteological terminology was based on Reis (1998), except for the use of parieto-supraoccipital instead of supraoccipital (Arratia, Gayet, 1995), pterotic-extrascapular instead of pterotic-supracleithrum (Slobodian, Pastana, 2018), and scapulocoracoid instead of coracoid (Lundberg, 1970). Nomenclature of the latero-sensory canals and preopercular pores are according to Schaefer, Aquino (2000) and Schaefer (1988), respectively. The supra-preopercle sensu, Huysentruyt, Adriaens (2005) was treated here as a part of the hyomandibula according to Vera-Alcaraz (2013). To determine the development degree of the anterior laminar expansion of infraorbital 1 in relation to the nasal capsule, the specimen was positioned to maintain the largest diameter of the nasal capsule horizontally. The width of frontal bone was obtained at the same point as the least interorbital width. Vertebral counts include only free centra (i.e., post-Weberian complex), with the compound caudal centrum (preural 1+ ural 1) counted as a single element. The relative size of dorsal-, pectoral-, pelvic- and anal-fin rays is analyzed qualitatively, comparing each ray in erected position (fin fully abducted), with the largest fin element as the main reference. The last two dorsal-fin rays were counted as distinct elements. Pharyngeal teeth were counted on both sides of the branchial arches. In the photos illustrating c&s specimens, the apparent size of some structures may eventually be altered by the perspective from which the photo was taken (e.g., it was not possible to perfectly align the mesethmoid in the horizontal plane in all photographed specimens, especially in dorsal view). Terminology regarding initial development follows Nakatani et al. (2001); the size of specimens in initial development is exceptionally expressed in total length (TL).
In the description, numbers in parentheses represent the total number of specimens with those counts. Numbers with an asterisk refer to the counts of the holotype. Institutional abbreviations follow Sabaj (2023). Political geography data of the type material is presented in the following order: country, state and municipality. The conservation status of the new species was suggested using the categories and criteria of the International Union for Conservation of Nature guidelines (IUCN Standards and Petitions Subcommittee, 2022).
RESULTS
Hoplisoma noxium, new species
urn:lsid:zoobank.org:act:41A57515-5575-4D62-9C2D-BEDDFA9A7778
Corydoras sp. CW004. ―Grant, 2019:8 (brief discussion on morphological variations; photo in life). ―Tencatt et al., 2022a:2 (listed as a putative undescribed species). ―Tencatt et al., 2024:3 (listed as a putative undescribed species).
Corydoras sp. ‘CW004 Ancestor I’. ―Grant, 2019:9 (brief discussion on morphological variations; photo in life).
Corydoras sp. ‘CW004 Ancestor II’. ―Grant, 2019:9 (brief discussion on morphological variations; photo in life).
Corydoras sp. ‘CW004 Ancestor III’. ―Grant, 2019:9 (brief discussion on morphological variations; photo in life).
Corydoras sp. CW155. ―Grant, 2020:25 (breeding report; photo in life). ―Tencatt et al., 2022a:2 (listed as a putative undescribed species). ―Tencatt et al., 2024a:3 (listed as a putative undescribed species).
Corydoras sp. CW156. ―Grant, 2020:25 (photo in life). ―Tencatt et al., 2022a:2 (listed as a putative undescribed species). ―Tencatt et al., 2024a:3 (listed as a putative undescribed species).
Corydoras sp. CW167. ―Tencatt et al., 2022a:2 (listed as a putative undescribed species). ―Tencatt et al., 2024a:3 (listed as a putative undescribed species).
Holotype. MNRJ 55759, 54.8 mm SL, Brazil, Pará, Jacareacanga, igarapé do Buriti (locally known as igarapé Sonrizal), rio Tapajós basin, approx. 06°13’S 57°55’W, 3–11 Jul 2023, W. M. Ohara, L. F. C. T. Tencatt & M. Pinheiro.
Paratypes. All from Brazil, Pará, Jacareacanga, rio Tapajós basin, 3–11 Jul 2023, except when noted. CPUFMT 8619, 4, 27.9–38.1 mm SL; INPA 61189, 4, 30.7–41.4 mm SL, igarapé Miuçuzinho, approx. 06°13’S 57°55’W, W. M. Ohara, L. F. C. T. Tencatt & M. Pinheiro. MNRJ 55760, 5, 47.3–58.4 mm SL; INPA 61188, 4, 39.5–56.4 mm SL, igarapé do Pinto, approx. 05°51’S 57°40’W, collected by local fishermen. INPA 61169, 10, 31.5–53.8 mm SL; MNRJ 55905, 15, 36.2–56.1 mm SL, igarapé do Pinto, approx. 05°51’S 57°40’W, 4 May 2024, collected by local fishermen. CITL 1458, 5 of 7, 49.8–51.2 mm SL, 2 c&s of 7, 39.7–53.0 mm SL; MZUSP 130710, 5, 26.6–48.1 mm SL; NUP 25701, 4, 28.0–48.5 mm SL; INPA 61187, 2, 35.0–41.1 mm SL, all collected with the holotype.
Diagnosis.Hoplisoma noxium can be distinguished from its congeners, except for H. araguaiaense (Sands, 1990), H. burgessi (Axelrod, 1987), H. colossus (Tencatt, Grant & Bentley, 2023), H. concolor (Weitzman, 1961), H. esperanzae (Castro, 1987), H. evelynae (Rössel, 1963), H. eversi (Tencatt & Britto, 2016), H. granti (Tencatt, Lima & Britto, 2019), H. julii (Steindachner, 1906), H. melanistium (Regan, 1912), H. oiapoquense (Nijssen, 1972), H. parallelum (Burgess, 1993), H. pavanelliae (Tencatt & Ohara, 2016), H. polystictum (Regan, 1912), H. schwartzi (Rössel, 1963), H. surinamense (Nijssen, 1970), H. trilineatum (Cope, 1872), H. xinguense (Nijssen, 1972) and H.tenebrosum, new species, by having the ventral surface of trunk with small to relatively large coalescent platelets, forming a typical mosaic-like pattern (vs. platelets on the ventral surface of trunk, when present, small-sized and not coalescent, not forming a mosaic-like pattern); from H. araguaiaense, H. burgessi, H. colossus, H. concolor, H. esperanzae, H. evelynae, H. eversi, H. granti, H. julii, H. melanistium, H. oiapoquense, H. parallelum, H. pavanelliae, H. polystictum, H. schwartzi, H. surinamense, H. trilineatum,and H. xinguense by having small, whitish yellow or beige blotches at least on the predorsal portion of body (vs. small blotches, when present, dark brown or black); from Hoplisoma n. sp. (described below) by having the flanks covered by small dark brown or black blotches, which can be roughly longitudinally aligned and variably fused with each other, forming narrow, disrupted irregular lines, but not solid stripes (vs. two or three longitudinal dark brown or black stripes on flanks), and by typically having more numerous pale blotches on the body (vs. typically fewer pale blotches). The new species can be further distinguished from H. araguaiaense, H. eversi, H. granti, H. julii, H. pavanelliae, H. polystictum, H. trilineatum and H. xinguense by the presence of a large, smoothly arched dark brown or black patch extending from anterior portion of parieto-supraoccipital towards region of interopercle, transversally crossing the orbit and forming the typical mask-like blotch (vs. mask-like blotch absent); from H. burgessi, H. melanistium, H. oiapoquense, H. parallelum, H. pavanelliae, H. polystictum, and H. surinamense by having a mosaic-like pattern of plates entirely or almost entirely covering the ventral surface of trunk (vs. mosaic-like pattern of plates restricted to some portions of the ventral surface of trunk, representing up to about 50% of its area).
Hoplisoma noxium, holotype, MNRJ 55759, 54.8 mm SL, Jacareacanga, Pará, Brazil, igarapé do Buriti (locally known as igarapé Sonrizal), rio Tapajós basin.
Description. Morphometric data in Tab. 1. Head laterally compressed with convex dorsal profile, roughly triangular in dorsal view. Snout moderately to relatively well developed, typically somewhat straight; smoothly rounded or pointed in some specimens. Head profile convex from tip of snout to anterior nares, ascending nearly straight or slightly convex from this point to dorsal-fin origin; region of posterior process of parieto-supraoccipital slightly convex in some specimens; region of anterior portion of mesethmoid and/or region of frontal fontanel variably slightly concave. Profile nearly straight to slightly convex along dorsal-fin base. Postdorsal-fin body profile slightly concave to adipose-fin spine, concave from this point to caudal-fin base; region between dorsal and preadipose platelets ranging from smoothly concave to smoothly convex. Ventral profile of body nearly straight or slightly convex from isthmus to pectoral girdle, and slightly convex from this point until pelvic girdle. Profile nearly straight to slightly convex from pelvic girdle to base of first anal-fin ray, ascending concave until caudal-fin base. Body roughly elliptical in cross section at pectoral girdle, gradually becoming more compressed toward caudal fin. Highest body depth at vertical through anterior dorsal-fin origin.
Eye rounded, located dorsolaterally on head. Orbit delimited anteriorly by lateral ethmoid, anterodorsally by frontal, posterodorsally by sphenotic, posteroventrally by infraorbital 2, and anteroventrally by infraorbital 1 (Fig. 2). Anterior and posterior nares close to each other, separated only by flap of skin. Anterior naris tubular. Posterior naris close to anterodorsal margin of orbit, separated from it by distance similar to naris diameter. Mouth small, subterminal, width similar to bony orbit diameter. Maxillary barbel length ranging from moderate, not reaching anteroventral limit of gill opening, to relatively long, slightly surpassing anteroventral limit of gill opening. Outer mental barbel typically slightly longer than maxillary barbel; outer mental barbel sometimes shorter than maxillary barbel, apparently due to barbel damage. Inner mental barbel fleshy, base of each counterpart slightly separated from each other. Area at mouth corner, ventral to maxillary barbel, typically with small wrinkle of skin (Fig. 3). Small rounded papillae covering entire surface of all barbels, upper and lower lips, snout and isthmus.
Mesethmoid moderate in size, its length slightly smaller than frontal length; anterior tip roughly straight in lateral view, relatively short, slightly smaller than 50% of bone length; posterior margin relatively narrow, its width smaller than maximum width of posterior portion of bone; base relatively short, lateral posterodorsal expansion with relatively wide roughly triangular or trapezoid external projection, emerging relatively close to distal point of suture with frontal; external projection relatively long in size, its distal tip slightly surpassing outermost margin of nasal bone; posterodorsal portion partially exposed and bearing small odontodes; posterior ventrolateral expansion partially visible in dorsal view, emerging slightly anteriorly to external projection of lateral posterodorsal expansion (Fig. 4). Upper and lower jaws edentulous; premaxilla overall funnel-like shaped, with anteroventral surface roughly triangular- to square-shaped in frontal view; anteroventral margin irregular; posterodorsal portion with conspicuous pointed process, mesially set in frontal view (Fig. 5); maxilla elongated, relatively slender and roughly hatchet shaped in frontal view, its proximal half with roughly trapezoid to rounded laminar process on posterolateral portion (Fig. 5); dentary relatively slender, with roughly trapezoid to triangular expansion on its anteroventral portion, in ventrolateral perspective, smoothly bent anteriorly, with distal edge variably smoothly curved posteriorly; roughly triangular process on its posterodorsal portion, bent posteriorly; angulo-articular moderately deep in its middle portion, with roughly triangular to rounded dorsal laminar expansion, its deepest area just posterior to posterodorsal margin of dentary; posteroventral portion with roughly triangular process, in lateral view, bent posteriorly (Fig. 5). Palatine longitudinally elongated, moderate-sized, with roughly triangular to rounded or trapezoid dorsolateral laminar expansion on its posterior portion, articulating with lateroventral expansion of posterior portion of mesethmoid; posterolateral process well developed, extending posteriorly in parallel to dorsal margin of anterior laminar expansion of metapterygoid (Fig. 4).
Morphometric data of the holotype and 14 paratypes of Hoplisoma noxium. SD = Standard deviation.
Head osteological pattern in a c&s paratype of Hoplisoma noxium (CITL 1458, 53.0 mm SL), showing (A) general morphology in lateral view, (B) infraorbital series in lateral view, and (C) region of orbit in dorsal view. Abbreviations: f: frontal, fdbp: first dorsolateral body plate, io1–2: infraorbital 1 and 2, iop: interopercle, le: lateral ethmoid, n: nasal, me: mesethmoid, op: opercle, pes: pterotic-extrascapular, pop: preopercle, prh: posterodorsal ridge of hyomandibula, pso: parieto-supraoccipital, sph: sphenotic. Yellow arrows indicate the inner laminar expansion of both infraorbitals. Area where the illustrated bones are located in fish’s body marked in red in the miniature photo of a paratype (CITL 1458, 51.2 mm SL) in life. Scale bars = 1 mm.
Detail of the snout in (A) the holotype of Hoplisoma noxium (MNRJ 55759, 54.8 mm SL), and (B) the holotype of Hoplisoma n. sp. (described below, MNRJ 55757, 52.5 mm SL), showing the small wrinkle (outlined in black) of skin at mouth corner, ventral to maxillary barbel. Area where the illustrated structure is located in fish’s body marked in red in (A) the miniature photo of a paratype of H. noxium (CITL 1458, 51.2 mm SL), and (B) miniature photo of the holotype of H. tenebrosum, both photographed alive. Scale bars = 1 mm.
Nasal capsule delimited posteriorly and dorsally by frontal, anteriorly by mesethmoid, and ventrally and posteriorly by lateral ethmoid (Fig. 4). Nasal slender, laterally curved, inner margin typically with moderately-developed laminar expansion, contacting frontal and mesethmoid; outer margin with strongly reduced laminar expansion (Figs. 2, 4, 6); juvenile c&s specimen (CITL 1458, 39.7 mm SL; dorso- and ventrolateral body plates not contacting counterparts on region between dorsal and adipose fins and pelvic and anal fins, respectively) with conspicuously smaller nasal laminar expansions, inner margin contacting only frontal. Lateral ethmoid moderately deep in lateral view, moderately expanded anteroventrally, with anterodorsal expansion slightly separated from nasal, and anterior margin contacting external projection of lateral posterodorsal expansion of mesethmoid (Figs. 2, 4); slender in lateral view, with anterodorsal expansion slightly more distant from nasal in juvenile specimen (CITL 1458, 39.7 mm SL); partially exposed and bearing small odontodes in some specimens. Frontal elongated, narrow, width less than half of entire length; anterior projection short, size smaller than nasal length (Fig. 6). Frontal fontanel large, slender, and somewhat ellipsoid; posterior tip extension slightly surpassing anterior margin of parieto-supraoccipital (Figs. 2, 6). Sphenotic somewhat trapezoid, contacting parieto-supraoccipital dorsally, pterotic-extrascapular posteriorly, second infraorbital posteroventrally and frontal anteriorly (Figs. 2, 6). Pterotic-extrascapular roughly pipe-shaped, with posteriormost portion contacting first lateral-line ossicle, posteroventral margin contacting cleithrum, and anteroventral margin contacting opercle and typically infraorbital 2; posterior expansion almost entirely covering lateral opening of swimbladder capsule, leaving slender area on its dorsal margin covered only by thick layer of skin (Fig. 2). Parieto-supraoccipital wide, posterior process long, contacting nuchal plate; region of contact between posterior process and nuchal plate covered by thick layer of skin (Fig. 6).
Cranial osteology in a c&s paratype of Hoplisoma noxium (CITL 1458, 53.0 mm SL), showing (A) the detail of mesethmoid in dorsal view, (B) the anterior portion of neurocranium in lateral view, and (C) the palatine in dorsal view. Abbreviations: eplp: external projection of lateral posterodorsal expansion of mesethmoid, f: frontal, le: lateral ethmoid, me: mesethmoid, n: nasal, pes: pterotic-extrascapular, pve: ventrolateral expansion of posterior portion of mesethmoid, sph: sphenotic. Black line in (C) outlining dorsolateral longitudinal laminar expansion of palatine. Area where the illustrated bones are located in fish’s body marked in red in the miniature photo of a paratype (CITL 1458, 51.2 mm SL) in life. Scale bars = 1 mm.
Cranial osteology in a c&s paratype of Hoplisoma noxium (CITL 1458, 53.0 mm SL), showing (A) the upper jaw in frontal view (= dorsal view considering everted mouth), and (B) the suspensorium plus operculum in lateral view. Abbreviations: aa: angulo-articular, d: dentary, hym: hyomandibula, iop: interopercle, mp: metapterygoid, mx: maxilla, op: opercle, pmx: premaxilla, pop: preopercle, prh: posterodorsal ridge of hyomandibula, q: quadrate. Red arrow indicates laminar process on posterolateral portion of maxilla; yellow and green arrows indicate anteroventral expansion and posterodorsal process of dentary, respectively; orange and blue arrows indicate dorsal laminar expansion and posteroventral process of angulo-articular, respectively. Area where the illustrated bones are located in fish’s body marked in red in the miniature photo of a paratype (CITL 1458, 51.2 mm SL) in life. Scale bars = 1 mm.
Top of head and predorsal region of trunk of a c&s paratype of Hoplisoma noxium (CITL 1458, 53.0 mm SL) in dorsal view. Abbreviations: f: frontal, n: nasal, np: nuchal plate, pes: pterotic-extrascapular, pso: parieto-supraoccipital, sph: sphenotic. Area where the illustrated bones are located in fish’s body marked in red in the miniature photo of the preserved holotype (MNRJ 55759, 54.8 mm SL) in dorsal view. Scale bar = 1 mm.
Two laminar infraorbitals with minute odontodes. Infraorbital 1 large, ventral laminar expansion typically ranging from well-developed to extremely well developed (Fig. 2); smaller specimens (up to about 40.0 mm SL) typically with moderately-developed ventral expansion; anterior portion with conspicuously well-developed laminar expansion, slightly surpassing anterior margin of nasal capsule; anterior laminar expansion well developed, surpassing middle of nasal capsule in juvenile specimen (CITL 1458, 39.7 mm SL); inner laminar expansion poorly developed (Fig. 2). Infraorbital 2 small, relatively slender, with posterior laminar expansion moderately to well developed (Fig. 2); posteroventral margin contacting posterodorsal ridge of hyomandibula, posterior margin close but not in direct contact with opercle, and posterodorsal edge contacting sphenotic and pterotic-extrascapular (Fig. 2); posterodorsal portion with roughly triangular to trapezoid expansion, and middle portion with moderately-developed roughly triangular expansion, smoothly bent downwards (Fig. 2), with tip just above dorsal edge of posterodorsal ridge of hyomandibula (Fig. 2); inner laminar expansion poorly developed (Fig. 2); infraorbital 2 laminar expansions clearly reduced in juvenile specimen (CITL 1458, 39.7 mm SL), especially posterior one, which lacks secondary expansions on posterodorsal and middle portions. Posterodorsal ridge of hyomandibula close to its articulation with opercle slender, exposed, and bearing small odontodes (Figs. 2, 6). Dorsal ridge of hyomandibula between pterotic-extrascapular and opercle covered by thick layer of skin, variably exposed and bearing small odontodes. Interopercle entirely or almost entirely covered by thick layer of skin; posterior portion variably exposed and bearing odontodes; subtriangular, anterior projection well developed (Figs. 2, 6). Preopercle elongated, relatively slender; minute odontodes on external surface (Figs. 2, 6). Opercle dorsoventrally elongated, with width slightly smaller than half of its entire length; free margin convex, without serrations and covered by small odontodes (Figs. 2, 6).
Four branchiostegal rays decreasing in size posteriorly. Hypobranchial 1 deep; hypobranchial 2 somewhat triangular, tip ossified and directed towards anterior portion, posterior margin cartilaginous; ossified portion well developed, its size about twice cartilaginous portion. Five ceratobranchials with expansions increasing posteriorly; ceratobranchial 1 with small process on anterior margin of mesial portion; ceratobranchial 3 notched on postero-lateral margin; ceratobranchial 5 toothed on posterodorsal surface, with 35 to 48 (2) teeth aligned in one row. Four epibranchials with similar size; epibranchial 2 slightly larger than others, with small, pointed process on laminar expansion of posterior margin; epibranchial 3 with mesially-curved uncinate process on laminar expansion of posterior margin. Two wide pharyngobranchials (3 and 4); pharyngobranchial 3 with roughly triangular laminar expansion on posterior margin; laminar expansion variably notched. Upper tooth plate roughly oval, 40 to 53 (2) teeth aligned in two rows on posteroventral surface; rows closely aligned.
Lateral-line canal reaching cephalic laterosensory system through pterotic-extrascapular, branching twice before reaching sphenotic: pterotic branch, with single pore, preoperculomandibular branch conspicuously reduced, with single pore opening at postotic main canal; postotic main canal widens just posterior to pterotic branch. Sensory canal continuing through pterotic-extrascapular, reaching sphenotic as temporal canal, which splits into two branches: one branch giving rise to infraorbital canal, the other branch connecting to frontal through supraorbital canal, both with single pore. Supraorbital canal branched, running through nasal bone. Epiphyseal branch conspicuously reduced; pore opening close to supraorbital main canal, directed towards frontal fontanel. Nasal canal with three openings, first on posterior edge, second on posterolateral portion and variably fused with first pore, and third on anterior edge. Infraorbital canal running through entire infraorbital 2, extending to infraorbital 1 and typically opening into two pores; variably into three pores. Preoperculomandibular branch giving rise to preoperculo-mandibular canal, which runs through almost entire preopercle with three openings, leading to pores 3, 4, and 5, respectively.
Dorsal fin subtriangular, typically located just posterior to second dorsolateral body plate. Dorsal-fin rays II,7(1), II,8*(14), with first branched ray as longest fin element; branched rays typically decreasing in size posteriorly, with first and second, and variably third, branched rays slightly longer than ossified portion of dorsal-fin spine, remaining rays with similar size or shorter than spine; first and second branched ray similar in size to ossified portion of spine in some specimens, with second branched ray variably shorter than spine; branched rays on middle portion of dorsal fin smaller than adjacent rays in some specimens, forming notch on dorsal-fin posterior margin; first and second branched rays variably clearly more elongated than spine, especially in juvenile specimens (up to about 40.0 mm SL); posterior margin of dorsal-fin spine with six to 21 strongly reduced to poorly-developed serrations; most serrations antrorse; some serrations variably perpendicularly directed (relative to main axis of spine), especially on distal portion of spine; bifid serrations variably present; serrations absent close to origin of spine; small odontodes on anterior and lateral surfaces of spine (Fig. 7). Nuchal plate moderately developed, almost entirely exposed, with minute odontodes. Spinelet short; spine typically ranging from moderately developed, with adpressed distal tip slightly surpassing posterior origin of dorsal-fin base, to well developed, with adpressed distal tip clearly surpassing posterior origin of dorsal-fin base; some specimens with poorly-developed spine, with adpressed distal tip not reaching posterior origin of dorsal-fin base. Pectoral fin roughly triangular, its origin just posterior to gill opening. Pectoral-fin I,8(4), I,9*(11), with first branched ray as longest fin element; branched rays decreasing in size posteriorly, with first and typically second branched rays slightly longer than ossified portion of pectoral-fin spine, remaining rays with similar size or shorter than spine; some specimens with second branched ray nearly equal in size to spine; posterior margin of pectoral spine with 13 to 28 strongly reduced to poorly-developed serrations along almost its entire length, absent close to origin of spine; typically, most serrations antrorse, with some serrations perpendicularly directed (relative to main axis of spine) and/or bifid; serrations fused at base variably present; some specimens with most serrations smoothly antrorse or roughly perpendicular in relation to main axis of spine; small odontodes on anterior, dorsal and ventral surfaces of spine (Fig. 7). Anteroventral portion of cleithrum and anterolateral portion of scapulocoracoid exposed; posterolateral portion of scapulocoracoid moderately developed, exposed, with anterior portion slightly expanded anteriorly, not in contact with anteroventral portion of cleithrum; exposed areas bearing small odontodes. Opening of axillary gland sensu Kiehl et al. (2006) located just posterior to pectoral-fin spine base.
Pelvic fin oblong, located just below first or second ventrolateral body plate, and at vertical through dorsal-fin spine or first dorsal-fin branched ray. Pelvic-fin rays i,5*(15); second branched ray typically as longest fin element, with rays decreasing in size towards both anterior and posterior margins of fin; second branched ray variably as long as first or third branched rays; unbranched ray as shorter fin element, or similar in size to last branched ray. Anterior internal process of basipterygium well developed and moderately laterally expanded, with obliquely placed dorsal lamina, converging mesially towards anterior edge of process; ventral laminar expansion obliquely placed, smoothly converging mesially towards anterior edge of process, clearly less developed than dorsal lamina; anterior external process laminar, moderately developed and slightly to moderately expanded posteriorly; dorsal ischiac process well developed, with anterior laminar expansion moderately expanded anteriorly, and posterior laminar expansion typically slightly expanded posteriorly; anterior and posterior laminar expansions of ischiac process roughly triangular or rounded; ventral ischiac process clearly smaller than dorsal process, roughly triangular, bent anteriorly (Fig. 8). Adipose fin roughly triangular, separated from base of last dorsal-fin ray by five to seven dorsolateral body plates. Anal fin subtriangular, located just posterior to 12th or 13th ventrolateral body plates, and at vertical through adipose-fin spine base or region of preadipose platelets. Anal-fin rays ii,5(10), i,6(4), ii,6*(1); third ray typically as longest fin element, with rays decreasing in size towards both anterior and posterior margins of fin; fourth ray variably similar in size to third ray; last ray typically as shorter fin element, variably similar in size to first ray. Caudal fin bilobed, with dorsal and ventral lobes similar in size or dorsal lobe slightly larger than ventral lobe; some specimens undergoing caudal regeneration with dorsal lobe smaller than ventral lobe. Caudal-fin rays i,11,i(2), i,12,i*(13), with generally four or five dorsal and ventral procurrent rays increasing in size posteriorly; small cartilage between upper principal and procurrent caudal-fin rays not observed (Fig. 9).
Lateral view of (A) the dorsal-fin spine and dorsal view of (B) the right pectoral-fin spine in a c&s paratype of Hoplisoma noxium (CITL 1458, 53.0 mm SL), showing their serration patterns. Area where the illustrated bones are located in fish’s body marked in red in the miniature photo of a paratype (CITL 1458, 51.2 mm SL) in life. Scale bars = 1 mm.
Pelvic girdle in two c&s paratypes of Hoplisoma noxium (CITL 1458), with (A) depicting specimen with 53.0 mm SL, and (B) 39.7 mm SL. Abbreviations: bp: basipterygium, pae: anterior external process, pai: anterior internal process, pi: dorsal ischiac process (damaged during dissection in B). Pelvic girdle position shown in red in the miniature photo of the preserved holotype (MNRJ 55759, 54.8 mm SL) in ventral view. Scale bars = 1 mm.
Three or four laterosensory canals on trunk; first ossicle tubular, second ossicle laminar, both bearing small odontodes; third and fourth encased in third and fourth dorsolateral body plates, respectively. Body plates with minute odontodes scattered over exposed area, with conspicuous line of odontodes confined to posterior margins. Dorsolateral body plates 23*(10), 24(5); ventrolateral body plates 20(3), 21*(10), 22(2). Dorsolateral body plates along dorsal-fin base 6(7), 7*(7), 8(1); dorsolateral body plates between adipose- and caudal-fin 6*(8), 7(7). Preadipose platelets 1(1), 2(8), 3*(6). Ventral surface of trunk between posteroventral margin of cleithrum and pelvic-fin origin typically laterally delimited only by first ventrolateral body plate; ventral portion of first ventrolateral body plate ranging from slightly to moderately expanded anteriorly. Small platelets covering base of caudal-fin rays; small platelets disposed dorsally and ventrally between junctions of lateral plates on posterior portion of caudal peduncle. Anterior margin of orbit, above region of junction between frontal and lateral ethmoid, and variably region around ventral margin of nasal capsule, with small- to relatively large-sized platelets bearing odontodes. Ventral surface of trunk mostly covered by small- to relatively large-sized coalescent platelets, forming typical mosaic-like pattern; platelets irregular in shape and bearing odontodes (Fig. 10).
General morphology of caudal skeleton in a c&s paratype of Hoplisoma noxium (CITL 1458, 53.0 mm SL). Abbreviations: ccc: compound caudal centrum, cfr: caudal-fin principal rays, dpcr: dorsal procurrent rays, epu: epural, has: haemal spine, hyp 1–5: hypurals 1 to 5, nes: neural spine, par: parhypural, pu 2–4: preural centra 2 to 4, un: uroneural, vpcr: ventral procurrent rays. Area where the illustrated bones are located in fish’s body marked in red in the miniature photo of a paratype (CITL 1458, 51.2 mm SL) in life. Scale bar = 1 mm.
Coalescent platelets on ventral surface of trunk in a c&s paratype of Hoplisoma noxium (CITL 1458, 53.0 mm SL), forming the typical mosaic-like pattern. Area in detail outlined (dotted line) in black in the miniature photo of the preserved holotype (MNRJ 55759, 54.8 mm SL) in ventral view. Scale bar = 1 mm.
Vertebral count 21(2); ribs 6(2); first pair conspicuously large, its middle portion closely connected to first ventrolateral body plate; its tip connected to anterior external process of basipterygium. Parapophysis of complex vertebra well developed.
Color in alcohol. Ground color of body brownish yellow to pale yellow or beige, with dorsal surface of head dark brown or black (Fig. 1). Dorsal and lateral surface of head, and lateral surface of cleithrum densely covered by dark brown or black chromatophores, not forming small dark blotches; lateral and dorsal surface of body anterior to dorsal fin with rounded, elliptical or vermiculated/irregular whitish to brownish yellow or pale yellow/beige blotches, variably spreading posteriorly, especially on dorsal portion of dorsolateral body plates around dorsal-fin base region and flank midline on anteriormost portion of trunk; pale blotches small to moderate in size, variably diffuse; large, smoothly arched dark brown or black patch extending from anterior portion of parieto-supraoccipital towards region of interopercle, transversally crossing orbit and forming typical mask-like blotch; mask-like blotch typically not reaching interopercle, ending on middle portion of preopercle; some specimens with less evident mask-like blotch; anterior portion of opercle with more concentrated dark brown or black chromatophores, especially on its ventral half, forming irregular dark patch, typically fused with mask-like blotch; opercular patch variably diffuse; lips and barbels with dark brown or black chromatophores, conspicuously more concentrated on upper lip and maxillary barbel; ventrolateral portion of head typically with dark brown or black chromatophores, with isthmus devoid of chromatophores; isthmus with scarce dark brown or black chromatophores in some specimens. Region of first dorsolateral body plate surrounding parieto-supraoccipital with conspicuous concentration of dark brown or black chromatophores, variably forming V-shaped pattern in dorsal view; some specimens with diffuse dark patch. Border of pores of laterosensory canals variably with conspicuous concentration of dark brown or black chromatophores. Anterodorsal portion of trunk, around anterior portion of dorsal-fin base, typically with relatively large, conspicuous dark brown or black blotch, clearly darker than ground color of body; blotch variably diffuse. Dorsal half of dorsolateral body plates with conspicuous concentration of dark brown or black chromatophores, forming small- to moderate-sized dark blotches, roughly longitudinally aligned. Portion of flank extending from ventral half of dorsolateral body plates to dorsal half of ventrolateral body plates with conspicuous concentrations of dark brown or black chromatophores, forming small- to moderate-sized dark blotches, typically roughly aligned in longitudinal rows, especially on region just above and just below flank midline; blotches longitudinally aligned around flank midline variably fused, forming narrow and irregular dark lines. Ventral half of ventrolateral body plates with less concentrated dark brown or black chromatophores, especially on region around pelvic-fin base, forming small-sized dark blotches in some specimens; blotches typically roughly aligned in longitudinal rows, variably diffuse. Dark blotches on flanks vertically fused, forming roughly transversally elongated blotches in some specimens. Posterior margin of body plates variably with conspicuous concentration of dark brown or black chromatophores, forming thin dark lines. Dorsal fin covered by dark brown or black chromatophores, conspicuously more concentrated on its anterior portion, especially between spine and third branched ray, typically forming dark patch, which is variably diffuse or absent; in specimens with anterior dark patch, remaining portion of fin with clearly less concentrated dark brown or black chromatophores, typically forming small-sized blotches, which can be elongated in parallel to main axis of rays (“dash-like”) or roughly rounded; dark blotches homogeneously scattered all over dorsal fin in specimens lacking anterior dark patch; blotches variably diffuse. Pectoral, pelvic, and anal fins with dark brown or black chromatophores, typically not forming blotches; chromatophores more concentrated on rays in some specimens; anal fin with small-sized dark markings in some specimens, similar in shape to dorsal-fin blotches and typically diffuse. Adipose fin covered by dark brown or black chromatophores, typically more concentrated on spine and posterior portion of membrane, forming one or more irregular dark patches, with moderate to relatively large size; patches variably diffuse. Caudal fin with dark brown or black chromatophores, conspicuously more concentrated on rays, typically forming small- to moderate-sized blotches, ranging from elongated in parallel to main axis of rays (“dash-like”) to roughly rounded; blotches diffuse, nearly imperceptible in some specimens; blotches variably roughly aligned in vertical rows, forming transversal dark stripes; middle portion of caudal-fin base with small irregular dark brown or black dot, variably diffuse; small platelets covering base of caudal-fin rays with conspicuous concentration of dark brown or black chromatophores, variably more concentrated on posterior portion of plates.
Color in life. Similar to color pattern of preserved specimens, but with brighter ground color of body (Figs. 11–14). Wild-caught specimens variably with light brownish orange coloration (Figs. 11, 12); aquarium specimens often with greyish yellow coloration (Figs. 13, 14). Additionally, both wild-caught and aquarium adult specimens variably with transversal dark stripe on posterior portion of caudal peduncle, just anterior to dark dot on middle portion of caudal-fin base, typical of specimens in early development (see Remarks section below) (Figs. 11, 13, 14). Body covered by greenish yellow iridescent coloration, especially on region of opercle and cleithrum.
Sexual dimorphism. Male specimens of Hoplisoma noxium present a genital papilla, which is somewhat tubular to conical, a condition well-documented in Corydoradinae (see Britto, 2003; Nijssen, Isbrücker, 1980b; Spadella et al., 2017). The presence of elongated two first dorsal-fin branched rays have been associated with dimorphic males of Hoplisoma (see Britto, Lima, 2003; Knaack, 2007; Tencatt et al., 2014a), a feature observed in some specimens of H. noxium. However, considering the available data, it was not possible to assign it as a sexually dimorphic feature as it seems to be more related to age/size, being mostly observed in juvenile specimens (up to about 40.0 mm SL).
Geographical distribution.Hoplisoma noxium is so far known from its type-locality, the igarapé do Buriti (= igarapé Sonrizal), igarapé Miuçuzinho and igarapé do Pinto, all tributaries of the rio Tapajós, rio Amazonas basin, Pará State, Brazil (Fig. 15).
Ecological notes. The igarapé do Buriti (= igarapé Sonrizal) (Fig. 16), type-locality of the new species, is a medium-sized tributary of the rio Tapajós characterized by having relatively clear tea-colored water, width ranging from about 10.0 m to about 30.0 m, depth typically not surpassing 1.5 m, and slow to moderate water current in the sampled sites. The substrate is mostly composed of sand and fine gravel, with stretches accumulating leaf litter and submerged logs/branches. Additionally, some stretches present submerged and marginal vegetation, including the partially exposed submerged roots of marginal trees. The igarapé Miuçuzinho is a relatively large tributary of the igarapé Muiuçu, itself a tributary of the rio Tapajós, characterized by having a relatively turbid water, with width around 20.0 to 30.0 m, and depth ranging from about 40 cm to more than 1.50 m, and substrate mostly composed by sand, with stretches accumulating leaf litter and submerged logs/branches, as well as partially exposed submerged roots of marginal trees, in the sampled site. In both localities, H. noxium was never observed during day time, being only observed, and captured during the night. The new species was observed by LFCT and WMO close to the margins, in sites with leaf litter and partially exposed submerged roots of marginal trees, in small numbers (up to four individuals) and relatively distant from each other. At the type-locality, H. noxium cooccurs with several other Corydoradinae species, namely: Brochis sp. C151 and CW176 (which we consider to be the same species), C. caramater, Corydoras sp. CW066 and CW174, and Hoplisoma sp. C152. In the igarapé Miuçuzinho, the new species cooccurs with Corydoras sp. CW174, Hoplisoma sp. C152 and CW193, while in the igarapé do Pinto it cooccurs only with Hoplisoma sp. CW193. Another interesting information on the new species was provided by the local fishermen, which reported that specimens of H. noxium must be separated from any other fish species just after capture, otherwise they can rapidly kill them, making the transport water milky and foamy on the surface, which was also observed by LFCT and WMO. Additionally, the same fisherman reported that getting “stung” by them (via dorsal and pectoral spines) is clearly more painful than any other Corydoradinae in the region, eventually causing minor allergic/inflammatory processes.
Variation of the color pattern in life in paratypes of Hoplisoma noxium, showing the general color pattern in lateral view of (A) CITL 1458, 51.2 mm SL, (B) CITL 1458, 50.8 mm SL, (C) INPA 61187, 41.1 mm SL, (D) INPA 61187, 35.0 mm SL, (E) INPA 61188, 56.4 mm SL, (F) INPA 61188, 53.8 mm SL, and (G) INPA 61188, 39.5 mm SL. Specimens (A–D) from the igarapé do Buriti, and (E–G) from the igarapé do Pinto. Photos by WMO.
Variation of the color pattern in life in paratypes of Hoplisoma noxium, showing the general color pattern in dorsal view of (A) INPA 61188, 53.8 mm SL, and (B) INPA 61188, 39.5 mm SL, both from the igarapé do Pinto. Photos by WMO.
Variation of the color pattern in life in uncatalogued and unmeasured aquarium specimens of Hoplisoma noxium recognized in the aquarium trade by the code CW004, in lateral view. Photo (A) by Hans Evers, photos (B) and (C) by Ingo Seidel.
Variation of the color pattern in life in uncatalogued and unmeasured aquarium specimens of Hoplisoma noxium recognized in the aquarium trade by the codes CW155 (A–D) and CW167 (E), in lateral view. Photo (A) by SG, (B) by Hans Evers, and photos (C–E) by Ingo Seidel.
Map showing the known geographic records of Hoplisoma noxium (red triangle: type-locality, igarapé do Buriti; black triangle: igarapé do Pinto) in Pará State, and the type-locality, the igarapé Água-branca, plus an additional record in the igarapé do Roncador of Hoplisoma tenebrosum (both represented by the green diamond) in Amazonas State, rio Tapajós basin, Brazil.
Etymology. The specific epithet “noxium” derives from the Latin “noxa”, a noun meaning “injury, damage”, plus “ium”, a Latin suffix used to form adjectives from nouns. The name alludes to the powerful toxin released by the new species under stress, which kills any fish kept in the same bag/container during transport. An adjective.
Conservation status. Currently, the new species is known only from its type-locality, the igarapé do Buriti (= igarapé Sonrizal), plus two additional records, the igarapé Miuçuzinho and the igarapé do Pinto, all tributaries of the rio Tapajós basin in Pará State, Brazil. Despite the relatively restricted geographical distribution, part of the drainage (headwaters) where the three streams flow is protected by some Conservation Units, especially the Floresta Nacional do Amaná, Floresta Nacional do Urupadi, and also by indigenous territories of the Munduruku ethnic group. Therefore, considering the currently available data and according to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN Standards and Petitions Subcommittee, 2022), Hoplisoma noxium would be classified as Least Concern (LC).
The igarapé do Buriti (= igarapé Sonrisal), type-locality of Hoplisoma noxium. Photo by WMO.
Remarks. Subtle differences in color pattern were observed in individuals of the three different populations examined herein, especially when comparing specimens from the type-locality with those from the igarapé do Pinto. Specimens from the igarapé do Buriti typically present more evident mask-like blotch and dark pigmentation associated with dorsal fin, i.e., on its anterior portion and on region around anterior portion of its base (Figs. 11A–D), while in the specimens from the igarapé do Pinto, such dark markings are typically less evident, or even absent in the case of the dark patches on dorsal fin (Figs. 11E–G). The specimens from the igarapé Miuçuzinho are more similar to those from the type-locality, but apparently tend to have more vertically elongated dark blotches on flanks.
Curiously, in both igarapé do Buriti and igarapé Miuçuzinho, the new species cooccurs with congeners with conspicuous mask-like blotch and dark blotches on anterior portion of dorsal fin and the region surrounding anterior portion of dorsal-fin base, especially Brochis sp. C151/CW176, Corydoras sp. CW174 and Hoplisoma sp. C152 (the first not captured in the igarapé Miuçuzinho). In the igarapé do Pinto, only Hoplisoma sp. CW193 was found to cooccur with the new species, which lacks a mask-like blotch and dark blotches on anterior portion of dorsal fin and the region surrounding anterior portion of dorsal-fin base. In this context, it is possible that the color pattern of the syntopic (regarding water body, not mesohabitat) species can, at least in part, explain the differences in color between different populations of H. noxium. Nevertheless, it is important to highlight that our observations on specimens from the igarapé Miuçuzinho are based on a small sample, composed only by four juvenile specimens (CPUFMT 8619, 27.9–38.1 mm SL).
Regarding snout morphology, H. noxium present a relatively wide range of variation, which can be moderately to relatively well developed, with dorsal profile slightly convex to somewhat straight or even slightly concave on region of anterior portion of mesethmoid, and anterior tip smoothly rounded or pointed (Figs. 1, 11, 13, 14, 17). Considering that specimens with different snout shapes, as well as slightly different color patterns, were found in the same population, and that, regardless of this, all of them share key features used to delimit species and/or genera within Corydoradinae, such as the morphology of the infraorbitals 1 and 2, dorsal- and pectoral-fin spines serrations, and mesethmoid (see Dias et al. (2024)); Description and Discussion sections), we considered them as congeneric and conspecific. This treatment diverges from current interpretation used in the aquarium trade, which is based essentially on the snout morphology, an approach that proved unreliable in the light of our analysis. As illustrated by previous studies (e.g., Tencatt et al., 2019; 2021; 2024a,b), the snout shape can conspicuously change along individual’s development, tending to become more pronounced with growth, which seems to be the case of H. noxium (Fig. 18). The specimen with more pronounced snout is the largest among paratypes (Fig. 17). Nevertheless, some species of Hoplisoma may present more pronounced snout in intermediary stages of development, with early and final stages displaying blunter snouts, as in congener H. thanatos (see Tencatt et al., 2022a:11, fig. 3).
Lateral view of the head in paratypes of Hoplisoma noxium, showing the variations in snout shape and size in (A) CITL 1458, 49.8 mm SL, (B) MNRJ 55760, 48.8 mm SL, (C) CITL 1458, 51.1 mm SL, and (D) MNRJ 55760, 58.4 mm SL. Specimens (A) and (C) from the igarapé do Buriti, (B) and (D) from the igarapé do Pinto.
Hoplisoma noxium has been bred under aquarium conditions by Roland van Ouwerkerk, who documented its ontogenetic development from 8.0 to 32.0 mm TL, showing general changes in external morphology and color pattern (Fig. 18). Considering the average quality of the several available photos, especially of the earliest stage (8.0 mm TL), the following description is focused mainly on general external morphology and color pattern. Even though only the photos that better illustrate the general aspect of each development stage were selected to compose Fig. 18, all of them were used for the following descriptions. Specimen with 8.0 mm TL apparently in early post-flexion stage (Fig. 18); head slightly depressed, becoming gradually deeper along individual’s growth; snout relatively short and rounded; eye moderate in size; median fin fold present, slightly absorbed, extending from posterior margin of dorsal fin to genital opening; dorsal, pectoral and caudal fins with distinct rays, including dorsal- and pectoral-fin spines; pelvic fin distinct, with presence of distinct rays uncertain; caudal-fin asymmetrical, its dorsal portion slightly longer than ventral. Body covered by dark brown or black chromatophores, more evident on head and anterior portion of dorsal-fin base; large, smoothly arched dark patch extending from anterior portion of parieto-supraoccipital towards region of interopercle, transversally crossing orbit and forming typical mask-like blotch; oblique dark stripe from anteroventral margin of orbit to upper lip lateral area, which gradually fades along individual’s growth. Flanks with slightly more diffuse dark markings, forming longitudinal series of moderate-sized blotches on flanks; middle portion of caudal-fin base with small irregular dark brown or black dot; diffuse transversal dark stripe on posterior portion of caudal peduncle, just anterior to dark dot on middle portion of caudal-fin base, which tends to be gradually less evident along individual’s growth, completely fading in some specimens; dorsal fin with diffuse roughly longitudinal dark stripes, and diffuse roughly transversal stripes on caudal fin.
Specimen with 10.0 mm TL apparently in early juvenile stage (Fig. 18), median fold apparently almost completely absorbed, with all fins more developed, especially adipose, pelvic, and anal fins; rays on pelvic and anal fins distinct, caudal fin smoothly bilobed; body plates apparently present. Body slightly more pigmented, with wider mask-like blotch; longitudinal series of moderate-sized dark blotches on flanks more evident and well defined; pectoral, pelvic and anal fins with small, diffuse dark blotches, which tend to fade along individual’s growth, especially on pectoral and pelvic fins. Specimen with 12.0 mm TL in early juvenile stage (Fig. 18), with fin fold completely absorbed, all fins clearly more developed; snout slightly more pronounced, body plates poorly developed; dark markings on flanks clearly smaller, except for some slightly larger blotches along flank midline and along dorsum, more evident around anterior portion of adipose fin; ill-defined whitish to brownish yellow or pale yellow/beige blotches apparently present on head, especially on its dorsal surface and opercle. Specimen with 32.0 mm TL in juvenile stage (Fig. 18), with more pronounced and pointed snout; caudal-fin ventral lobe more evident; body plates conspicuously more developed, apparently fully covering flanks; overall color pattern as described for fully-grown adults.
Ontogenetic series of Hoplisoma noxium (bred under aquarium conditions) showing general changes in external morphology and color pattern in specimens with (A) 8.0 mm TL, (B) 10.0 mm TL; (D) 12.0 mm TL, and (E) 32.0 mm TL. Photos by Roland van Ouwerkerk.
Hoplisoma tenebrosum, new species
urn:lsid:zoobank.org:act:1FCC2F89-DD75-4F3F-B38E-C98D5EFA0607
Corydoras sp. CW168. ―Tencatt et al., 2022a:2 (listed as a putative undescribed species). ―Tencatt et al., 2024a:3 (listed as a putative undescribed species).
Holotype. MNRJ 55757, 52.5 mm SL, Brazil, Amazonas, Maués, igarapé Água-branca (= Ipixuna) at the confluence with the igarapé Palomita, rio Tapajós basin, rio Amazonas basin, approx. 06°36’S 58°37’W, 3–11 Jul 2023, collected by local fishermen.
Hoplisoma tenebrosum, holotype, MNRJ 55757, 52.5 mm SL, Maués, Amazonas, Brazil, igarapé Água-branca (= Ipixuna) at the confluence with the igarapé Palomita, rio Tapajós basin.
Paratypes. All from Brazil, Amazonas, Maués, rio Tapajós basin, rio Amazonas basin, approx. 06°36’S 58°37’W, 3–11 Jul 2023, collected by local fishermen. CITL 1459, 5 of 6, 43.2–49.2 mm SL, 1 c&s of 6, 47.4 mm SL; INPA 61190, 3, 31.0–42.8 mm SL; MZUSP 130711, 4, 43.7–46.5 mm SL, igarapé do Roncador. CPUFMT 8620, 6, 29.3–49.7 mm SL; MNRJ 55758, 5 of 6, 32.4–49.2 mm SL, 1 c&s of 6, 54.6 mm SL; NUP 25702, 5, 31.2–51.4 mm SL, collected with holotype.
Diagnosis.Hoplisoma tenebrosum can be distinguished from its congeners, except for H. araguaiaense, H. burgessi, H. colossus, H. concolor, H. esperanzae, H. evelynae, H. eversi, H. granti, H. julii, H. melanistium, H. oiapoquense, H. parallelum, H. pavanelliae, H. polystictum, H. schwartzi, H. surinamense, H. trilineatum, H. xinguense and H.noxium by having the ventral surface of trunk with small- to relatively large-sized coalescent platelets, forming a typical mosaic-like pattern (vs. platelets on the ventral surface of trunk, when present, small-sized and not coalescent, not forming a mosaic-like pattern); from H. araguaiaense, H. burgessi, H. colossus, H. concolor, H. esperanzae, H. evelynae, H. eversi, H. granti, H. julii, H. melanistium, H. oiapoquense, H. parallelum, H. pavanelliae, H. polystictum, H. schwartzi, H. surinamense, H. trilineatum,and H. xinguense by having small, whitish to brownish yellow or pale yellow/beige blotches on the predorsal portion of body (vs. blotches on predorsal portion of body, when present, dark brown or black); from H. noxium by having two or three longitudinal dark brown or black stripes on flanks (vs. flanks covered by small dark brown or black blotches, which can be roughly longitudinally aligned and variably fused with each other, forming narrow irregular lines, but not solid stripes), and by typically having fewer pale blotches on the body (vs. typically more numerous pale blotches). The new species can be further distinguished from H. araguaiaense, H. eversi, H. granti, H. julii, H. pavanelliae, H. polystictum, H. trilineatum, and H. xinguense by the presence of a large, smoothly arched dark brown or black patch extending from the anterior portion of parieto-supraoccipital towards the region of interopercle, transversally crossing the orbit and forming a typical mask-like blotch (vs. mask-like blotch absent); from H. burgessi, H. melanistium, H. oiapoquense, H. parallelum, H. pavanelliae, H. polystictum and H. surinamense by having a mosaic-like pattern of plates entirely or almost entirely covering the ventral surface of trunk (vs. mosaic-like pattern of plates restricted to some portions of the ventral surface of trunk, representing up to about 50% of its area).
Description. Morphometric data in Tab. 2. Head laterally compressed with convex dorsal profile, roughly triangular in dorsal view. Snout moderately to relatively well developed and somewhat straight. Head profile convex from tip of snout to anterior nares, ascending nearly straight or slightly convex from this point to dorsal-fin origin; region of anterior portion of mesethmoid and/or region of frontal fontanel typically slightly concave. Profile nearly straight to slightly convex along dorsal-fin base. Postdorsal-fin body profile slightly concave to adipose-fin spine, concave from this point to caudal-fin base; region between dorsal and preadipose platelets nearly straight to slightly convex in some specimens. Ventral profile of body nearly straight or slightly convex from isthmus to pectoral girdle, and slightly convex from this point until pelvic girdle. Profile nearly straight to slightly convex from pelvic girdle to base of first anal-fin ray, ascending concave until caudal-fin base. Body roughly elliptical in cross section at pectoral girdle, gradually becoming more compressed toward caudal fin. Highest body depth at vertical through anterior dorsal-fin origin.
Eye rounded, located dorsolaterally on head. Orbit delimited anteriorly by lateral ethmoid, anterodorsally by frontal, posterodorsally by sphenotic, posteroventrally by infraorbital 2, and anteroventrally by infraorbital 1 (Fig. 20). Anterior and posterior nares close to each other, separated only by flap of skin. Anterior naris tubular. Posterior naris close to anterodorsal margin of orbit, separated from it by distance similar to naris diameter. Mouth small, subterminal, width similar to bony orbit diameter. Maxillary barbel length ranging from moderate, not reaching anteroventral limit of gill opening, to relatively long, slightly surpassing anteroventral limit of gill opening. Outer mental barbel slightly longer than maxillary barbel. Inner mental barbel fleshy, base of each counterpart slightly separated from each other. Area at mouth corner, ventral to maxillary barbel, typically with small wrinkle of skin (Fig. 3). Small rounded papillae covering entire surface of all barbels, upper and lower lips, snout and isthmus.
Morphometric data of the holotype and 14 paratypes of Hoplisoma tenebrosum. SD = Standard deviation.
Head osteological pattern in a c&s paratype of Hoplisoma tenebrosum (MNRJ 55758, 54.6 mm SL), showing (A) general morphology in lateral view, (B) infraorbital series in lateral view, and (C) region of orbit in dorsal view. Abbreviations: f: frontal, fdbp: first dorsolateral body plate, io1–2: infraorbital 1 and 2, iop: interopercle, le: lateral ethmoid, n: nasal, me: mesethmoid, op: opercle, pes: pterotic-extrascapular, pop: preopercle, prh: posterodorsal ridge of hyomandibula, pso: parieto-supraoccipital, sph: sphenotic. Yellow arrows indicate the inner laminar expansion of both infraorbitals. Area where the illustrated bones are located in fish’s body marked in red in the miniature photo of the holotype (MNRJ 55757, 52.5 mm SL) in life. Scale bars = 1 mm.
Mesethmoid moderate in size, its length slightly smaller than frontal length; anterior tip roughly straight in lateral view, relatively short, slightly smaller than 50% of bone length; posterior margin relatively narrow, its width smaller than maximum width of posterior portion of bone; base relatively short, lateral posterodorsal expansion with relatively wide roughly triangular or trapezoid external projection, emerging relatively close to distal point of suture with frontal; external projection relatively long in size, its distal tip slightly surpassing outermost margin of nasal bone; posterodorsal portion partially exposed and bearing small odontodes; posterior ventrolateral expansion partially visible in dorsal view, emerging slightly anteriorly to external projection of lateral posterodorsal expansion (Fig. 21). Upper and lower jaws edentulous; premaxilla overall funnel-like shaped, with anteroventral surface roughly square-shaped to slightly horizontally rectangular in frontal view; anteroventral margin irregular; posterodorsal portion with conspicuous pointed process, mesially set in frontal view (Fig. 22); maxilla elongated, relatively slender and roughly hatchet shaped in frontal view, its proximal half with roughly triangular laminar process on posterolateral portion (Fig. 22); dentary relatively slender, with roughly trapezoid to triangular expansion on its anteroventral portion, in ventrolateral perspective, smoothly bent anteriorly, with distal edge variably smoothly curved posteriorly; roughly triangular process on its posterodorsal portion, bent posteriorly; angulo-articular moderately deep in its middle portion, with roughly triangular to rounded dorsal laminar expansion, its deepest area just posterior to posterodorsal margin of dentary; posteroventral portion with roughly triangular process, in lateral view, bent posteriorly (Fig. 22). Palatine longitudinally elongated, moderate-sized, with roughly triangular dorsolateral laminar expansion on its posterior portion, articulating with lateroventral expansion of posterior portion of mesethmoid; posterolateral process well developed, extending posteriorly in parallel to dorsal margin of anterior laminar expansion of metapterygoid (Fig. 21).
Cranial osteology in a c&s paratype of Hoplisoma tenebrosum (MNRJ 55758, 54.6 mm SL), showing (A) the detail of mesethmoid in dorsal view, (B) the anterior portion of neurocranium in lateral view, and (C) the palatine in dorsal view. Abbreviations: eplp: external projection of lateral posterodorsal expansion of mesethmoid, f: frontal, le: lateral ethmoid, me: mesethmoid, n: nasal, pes: pterotic-extrascapular, pve: ventrolateral expansion of posterior portion of mesethmoid, sph: sphenotic. Black line in (C) outlining dorsolateral longitudinal laminar expansion of palatine. Area where the illustrated bones are located in fish’s body marked in red in the miniature photo of the holotype (MNRJ 55757, 52.5 mm SL) in life. Scale bars = 1 mm.
Cranial osteology in a c&s paratype of Hoplisoma tenebrosum (MNRJ 55758, 54.6 mm SL), showing (A) the upper jaw in frontal view (= dorsal view considering everted mouth), and (B) the suspensorium plus operculum in lateral view. Abbreviations: aa: angulo-articular, d: dentary, hym: hyomandibula, iop: interopercle, mp: metapterygoid, mx: maxilla, op: opercle, pmx: premaxilla, pop: preopercle, prh: posterodorsal ridge of hyomandibula, q: quadrate. Red arrow indicates laminar process on posterolateral portion of maxilla; yellow and green arrows indicate anteroventral expansion and posterodorsal process of dentary, respectively; orange and blue arrows indicate dorsal laminar expansion and posteroventral process of angulo-articular, respectively. Area where the illustrated bones are located in fish’s body marked in red in the miniature photo of the holotype (MNRJ 55757, 52.5 mm SL) in life.
Nasal capsule delimited posteriorly and dorsally by frontal, anteriorly by mesethmoid, and ventrally and posteriorly by lateral ethmoid. Nasal slender, laterally curved, inner margin typically with poorly-developed laminar expansion, contacting only frontal; outer margin with strongly reduced laminar expansion (Figs. 20, 21). Lateral ethmoid moderately deep in lateral view, moderately expanded anteroventrally, with anterodorsal expansion slightly separated from nasal, and anterior margin contacting external projection of lateral posterodorsal expansion of mesethmoid (Figs. 20, 21); partially exposed and bearing small odontodes in some specimens. Frontal elongated, narrow, width less than half of entire length; anterior projection short, size smaller than nasal length (Fig. 23). Frontal fontanel large, slender, and somewhat ellipsoid; posterior tip extension slightly surpassing anterior margin of parieto-supraoccipital (Figs. 23). Sphenotic somewhat trapezoid, contacting parieto-supraoccipital dorsally, pterotic-extrascapular posteriorly, second infraorbital posteroventrally and frontal anteriorly (Figs. 20, 23). Pterotic-extrascapular roughly pipe-shaped, with posteriormost portion contacting first lateral-line ossicle, posteroventral margin contacting cleithrum, and anteroventral margin contacting opercle and infraorbital 2; posterior expansion almost entirely covering lateral opening of swim bladder capsule, leaving slender area on its dorsal margin covered only by thick layer of skin (Fig. 20). Parieto-supraoccipital wide, posterior process long, contacting nuchal plate; region of contact between posterior process and nuchal plate covered by thick layer of skin (Fig. 23).
Two laminar infraorbitals with minute odontodes. Infraorbital 1 large, ventral laminar expansion typically ranging from well-developed to extremely well developed (Fig. 20); juvenile specimens (up to about 40.0 mm SL; dorso- and ventrolateral body plates not contacting counterparts on region between dorsal and adipose fins and pelvic and anal fins, respectively) with ventral laminar expansion ranging from poorly to moderately developed; anterior portion with well-developed laminar expansion, surpassing middle of nasal capsule, nearly reaching anterior margin of nasal capsule in some specimens; inner laminar expansion poorly developed (Fig. 20). Infraorbital 2 small, relatively slender, with posterior laminar expansion moderately to well developed (Fig. 20); posteroventral margin contacting posterodorsal ridge of hyomandibula, posterior margin close but not in direct contact with opercle, and posterodorsal edge contacting sphenotic and pterotic-extrascapular (Fig. 20); posterodorsal portion with roughly triangular to trapezoid expansion, and middle portion with poorly-developed and rounded to moderately-developed and roughly triangular expansion; when moderately developed, middle expansion smoothly bent downwards (Fig. 20), with tip just above dorsal edge of posterodorsal ridge of hyomandibula (Fig. 20); inner laminar expansion poorly developed (Fig. 20). Posterodorsal ridge of hyomandibula close to its articulation with opercle slender, exposed, and bearing small odontodes (Figs. 20, 22). Dorsal ridge of hyomandibula between pterotic-extrascapular and opercle covered by thick layer of skin, variably exposed and bearing small odontodes. Interopercle entirely or almost entirely covered by thick layer of skin; posterior portion variably exposed and bearing odontodes; subtriangular, anterior projection well developed (Figs. 20, 22). Preopercle elongated, relatively slender; minute odontodes on external surface (Figs. 20, 22). Opercle dorsoventrally elongated, with width slightly smaller than half of its entire length; free margin convex, without serrations and covered by small odontodes (Figs. 20, 22).
Top of head and predorsal region of trunk of a c&s paratype of Hoplisoma tenebrosum (MNRJ 55758, 54.6 mm SL) in dorsal view. Abbreviations: f: frontal, n: nasal, np: nuchal plate, pes: pterotic-extrascapular, pso: parieto-supraoccipital, sph: sphenotic. Area where the illustrated bones are located in fish’s body marked in red in the miniature photo of the preserved holotype (MNRJ 55757, 52.5 mm SL) in dorsal view. Scale bar = 1 mm.
Four branchiostegal rays decreasing in size posteriorly. Hypobranchial 1 deep; hypobranchial 2 somewhat triangular, tip ossified and directed towards anterior portion, posterior margin cartilaginous; ossified portion well developed, its size about twice cartilaginous portion. Five ceratobranchials with expansions increasing posteriorly; ceratobranchial 1 with small process on anterior margin of mesial portion; process variably strongly reduced; ceratobranchial 3 notched on postero-lateral margin; variably with continuous laminar expansion on postero-lateral margin; ceratobranchial 5 toothed on posterodorsal surface, with 47 to 49 (2) teeth aligned in one row. Four epibranchials with similar size; epibranchial 2 slightly larger than others, with small, pointed process on laminar expansion of posterior margin; epibranchial 3 with mesially-curved uncinate process on laminar expansion of posterior margin. Two wide pharyngobranchials (3 and 4); pharyngobranchial 3 with roughly triangular laminar expansion on posterior margin; laminar expansion variably notched. Upper tooth plate roughly oval, 50 to 58 (2) teeth aligned in two rows on posteroventral surface; rows closely aligned.
Lateral-line canal reaching cephalic laterosensory system through pterotic-extrascapular, branching twice before reaching sphenotic: pterotic branch, with single pore, preoperculomandibular branch conspicuously reduced, with single pore opening at postotic main canal; postotic main canal widens just posterior to pterotic branch. Sensory canal continuing through pterotic-extrascapular, reaching sphenotic as temporal canal, which splits into two branches: one branch giving rise to infraorbital canal, the other branch connecting to frontal through supraorbital canal, both with single pore. Supraorbital canal branched, running through nasal bone. Epiphyseal branch conspicuously reduced; pore opening close to supraorbital main canal, directed towards frontal fontanel. Nasal canal with three openings, first on posterior edge, second on posterolateral portion and typically fused with first pore, and third on anterior edge. Infraorbital canal running through entire infraorbital 2, extending to infraorbital 1 and typically opening into two pores. Preoperculomandibular branch giving rise to preoperculo-mandibular canal, which runs through almost entire preopercle with three openings, leading to pores 3, 4, and 5, respectively.
Dorsal fin subtriangular, typically located just posterior to second dorsolateral body plate. Dorsal-fin rays II,7(1), II,8*(9), II,9(5), with first branched ray as longest fin element; branched rays decreasing in size posteriorly, with first and second, and variably third, branched rays slightly longer than ossified portion of dorsal-fin spine, remaining rays with similar size or shorter than spine; branched rays on middle portion of dorsal fin smaller than adjacent rays in some specimens, forming notch on dorsal-fin posterior margin; first and second branched rays clearly more elongated than spine in some specimens; posterior margin of dorsal-fin spine with 18 to 24 strongly reduced to poorly-developed serrations; most serrations antrorse; some serrations variably perpendicularly directed (relative to main axis of spine), especially on distal portion of spine; serrations absent close to origin of spine; small odontodes on anterior and lateral surfaces of spine (Fig. 24). Nuchal plate moderately developed, almost entirely exposed, with minute odontodes. Spinelet short; spine typically well developed, with adpressed distal tip clearly surpassing posterior origin of dorsal-fin base; variably moderately developed, with adpressed distal tip slightly surpassing posterior origin of dorsal-fin base. Pectoral fin roughly triangular, its origin just posterior to gill opening. Pectoral-fin I,8(4), I,9(8), I,9,i(1), I,10*(2), with first branched ray as longest fin element; branched rays decreasing in size posteriorly, with first and typically second branched rays slightly longer than ossified portion of pectoral-fin spine, remaining rays with similar size or shorter than spine; some specimens with second branched ray nearly equal in size to spine; posterior margin of pectoral spine with 26 to 33 strongly reduced to poorly-developed serrations along almost its entire length, absent close to origin of spine; typically, most serrations antrorse, with some serrations perpendicularly directed (relative to main axis of spine) and/or bifid; serrations fused at base variably present; some specimens with most serrations smoothly antrorse, nearly perpendicular in relation to main axis of spine; small odontodes on anterior, dorsal and ventral surfaces of spine (Fig. 24). Anteroventral portion of cleithrum and anterolateral portion of scapulocoracoid exposed; posterolateral portion of scapulocoracoid moderately developed, exposed, with anterior portion slightly expanded anteriorly, not in contact with anteroventral portion of cleithrum; exposed areas bearing small odontodes. Opening of axillary gland sensu Kiehl et al. (2006) located just posterior to pectoral-fin spine base.
Pelvic fin oblong, located just below first or second ventrolateral body plate, and at vertical through first or second dorsal-fin branched ray. Pelvic-fin rays i,5*(15); second branched ray typically as longest fin element, with rays decreasing in size towards both anterior and posterior margins of fin; third branched ray variably as long as second branched ray; unbranched ray typically as shorter fin element. Anterior internal process of basipterygium well developed and ranging from slightly to moderately laterally expanded, with obliquely placed dorsal lamina, converging mesially towards anterior edge of process; ventral laminar expansion obliquely placed, smoothly converging mesially towards anterior edge of process, clearly less developed than dorsal lamina; anterior external process laminar, moderately developed and slightly to moderately expanded posteriorly; dorsal ischiac process well developed, with anterior laminar expansion moderately expanded anteriorly, and posterior laminar expansion slightly to moderately expanded posteriorly; anterior and posterior laminar expansions of ischiac process roughly triangular or rounded; ventral ischiac process clearly smaller than dorsal process, roughly triangular, bent anteriorly (Fig. 25). Adipose fin roughly triangular, separated from base of last dorsal-fin ray by six or seven dorsolateral body plates. Anal fin subtriangular, located just posterior to 11th, 12th or 13th ventrolateral body plates, and at vertical through adipose-fin spine base or region of preadipose platelets. Anal-fin rays ii,5*(10), i,6(1), i,6,i(1), ii,6(2), single specimen with ii,2,i, possibly due to malformation; third or fourth ray as the longest fin element, with rays decreasing in size towards both anterior and posterior margins of fin; first or last ray as shorter fin element. Caudal fin bilobed, with dorsal and ventral lobes similar in size or dorsal lobe slightly larger than ventral lobe; some specimens undergoing caudal regeneration with dorsal lobe smaller than ventral lobe. Caudal-fin rays i,12,i*(13), i,13,i(1), single specimen with i,5,i,1,i,7,i (possibly due to malformation), with generally four or five dorsal and ventral procurrent rays increasing in size posteriorly; small cartilage between upper principal and procurrent caudal-fin rays not observed (Fig. 26).
Lateral view of (A) the dorsal-fin spine and dorsal view of (B) the left pectoral-fin spine in a c&s paratype of Hoplisoma tenebrosum (MNRJ 55758, 54.6 mm SL), showing their serration patterns. Area where the illustrated bones are located in fish’s body marked in red in the miniature photo of the holotype (MNRJ 55757, 52.5 mm SL) in life. Scale bars = 1 mm.
Pelvic girdle in two c&s paratypes of Hoplisoma tenebrosum, with (A) depicting specimen CITL 1459, 47.4 mm SL, and (B) MNRJ 55758, 54.6 mm SL. Abbreviations: bp: basipterygium, pae: anterior external process, pai: anterior internal process, pi: dorsal ischiac process. Pelvic girdle position shown in red in the miniature photo of the preserved holotype (MNRJ 55757, 52.5 mm SL) in ventral view. Scale bars = 1 mm.
Two to four laterosensory canals on trunk; first ossicle tubular, second ossicle laminar, both bearing small odontodes; third and fourth, if present, encased in third and fourth dorsolateral body plates, respectively. Body plates with minute odontodes scattered over exposed area, with conspicuous line of odontodes confined to posterior margins. Dorsolateral body plates 22(3), 23*(9), 24(3); ventrolateral body plates 19(1), 20*(8), 21(6). Dorsolateral body plates along dorsal-fin base 6 (4), 7* (11); dorsolateral body plates between adipose- and caudal-fin 5(1), 6*(10), 7(4). Preadipose platelets 2(9), 3*(5). Ventral surface of trunk between posteroventral margin of cleithrum and pelvic-fin origin typically laterally delimited only by first ventrolateral body plate; ventral portion of first ventrolateral body plate ranging from slightly to moderately expanded anteriorly. Small platelets covering base of caudal-fin rays; small platelets disposed dorsally and ventrally between junctions of lateral plates on posterior portion of caudal peduncle. Anterior margin of orbit, above region of junction between frontal and lateral ethmoid, variably with small- to moderate-sized platelets bearing odontodes. Ventral surface of trunk mostly covered by small- to relatively large-sized coalescent platelets, forming typical mosaic-like pattern; platelets irregular in shape and bearing odontodes (Fig. 27).
General morphology of caudal skeleton in a c&s paratype of Hoplisoma tenebrosum (CITL 1459, 47.4 mm SL). Abbreviations: ccc: compound caudal centrum, cfr: caudal-fin principal rays, dpcr: dorsal procurrent rays, epu: epural, has: haemal spine, hyp 1–5: hypurals 1 to 5, nes: neural spine, par: parhypural, pu 2–4: preural centra 2 to 4, un: uroneural, vpcr: ventral procurrent rays. Area where the illustrated bones are located in fish’s body marked in red in the miniature photo of the holotype (MNRJ 55757, 52.5 mm SL) in life. Scale bar = 1 mm.
Coalescent platelets on ventral surface of trunk in a c&s paratype of Hoplisoma tenebrosum (CITL 1459, 47.4 mm SL), forming the typical mosaic-like pattern. Area in detail outlined (dotted line) in black in the miniature photo of the preserved holotype (MNRJ 55757, 52.5 mm SL) in ventral view. Scale bar = 1 mm.
Vertebral count 21(1), 22(1); ribs 6(1), 7(1); first pair conspicuously large, its middle portion closely connected to first ventrolateral body plate; its tip connected to anterior external process of basipterygium. Parapophysis of complex vertebra well developed.
Color in alcohol. Ground color of body brownish yellow to pale yellow or beige, with dorsal surface of head dark brown or black (Fig. 19). Dorsal and lateral surface of head, and lateral surface of cleithrum densely covered by dark brown or black chromatophores, not forming small dark blotches; lateral and dorsal surface of body anterior to dorsal fin with rounded, elliptical or vermiculated/irregular whitish to brownish yellow or pale yellow/beige blotches, especially on snout and posterodorsally to orbit; pale blotches small to moderate in size, variably scarce and/or diffuse; large, smoothly arched dark brown or black patch extending from anterior portion of parieto-supraoccipital towards region of interopercle, transversally crossing orbit and forming typical mask-like blotch; mask-like blotch typically not reaching interopercle, ending on middle portion of preopercle; some specimens with less evident mask-like blotch; anterior portion of opercle with more concentrated dark brown or black chromatophores, especially on its ventral half, forming irregular dark patch, typically fused with mask-like blotch; opercular patch variably diffuse; lips and barbels with dark brown or black chromatophores, conspicuously more concentrated on upper lip and maxillary barbel; ventrolateral portion of head typically with dark brown or black chromatophores, with isthmus devoid of chromatophores; isthmus with scarce dark brown or black chromatophores in some specimens. Region of first dorsolateral body plate surrounding parieto-supraoccipital with conspicuous concentration of dark brown or black chromatophores, variably forming V-shaped pattern in dorsal view; some specimens with diffuse dark patch. Border of pores of laterosensory canals variably with conspicuous concentration of dark brown or black chromatophores. Anterodorsal portion of trunk, around anterior portion of dorsal-fin base, with relatively large, dark brown or black blotch, clearly darker than ground color of body. Dorsal portion of dorsolateral body plates with conspicuous concentration of dark brown or black chromatophores, variably forming dorsal longitudinal stripe or roughly longitudinally aligned dark blotches; dorsal stripe fragmented in some specimens; region of dorsolateral body plates just above midline of flank with conspicuous concentration of dark brown or black chromatophores, forming dark longitudinal stripe extending from region at vertical through anterior portion of dorsal-fin base to caudal-fin base; mid-dorsolateral stripe not reaching caudal-fin base and/or fragmented posteriorly in some specimens; dorsal and mid-dorsolateral stripe variably fused with dark blotch on anterior portion of dorsal-fin base; remaining portions of dorsolateral body plates clearly paler, with conspicuously less concentrated dark brown or black chromatophores. Region of ventrolateral body plates just below midline of flank with conspicuous concentration of dark brown or black chromatophores, forming dark longitudinal stripe extending from region at vertical through anterior portion of dorsal-fin base to caudal-fin base; mid-ventrolateral stripe not reaching caudal-fin base and/or fragmented posteriorly in some specimens; remaining portions of ventrolateral body plates paler, with conspicuously less concentrated dark brown or black chromatophores, especially on region around pelvic-fin base; mid-dorsolateral and mid-ventrolateral stripes ranging from slender to wide; some specimens with ventral half of ventrolateral body plates on region between pelvic and anal fins with conspicuous concentration of dark brown or black chromatophores, forming rounded, irregular or vertically elongated blotches, roughly aligned longitudinally and variably diffuse. Middle portion of flank, especially on anterior half of trunk, with small dark brown or black blotches in some specimens. Posterior margin of body plates variably with conspicuous concentration of dark brown or black chromatophores, forming thin dark lines. Dorsal fin covered by dark brown or black chromatophores, conspicuously more concentrated on its anterior portion, especially between spine and third branched ray, forming dark patch, which is variably diffuse; remaining portion of fin with clearly less concentrated dark brown or black chromatophores, variably forming small- to moderate-sized blotches; dorsal-fin blotches typically elongated in parallel to main axis of rays (“dash-like”), variably roughly rounded and/or diffuse. Pectoral, pelvic, and anal fins with dark brown or black chromatophores, typically more concentrated on rays and not forming blotches; anal fin with small- to moderate-sized dark markings in some specimens, typically elongated in parallel to main axis of rays (“dash-like”) and diffuse. Adipose fin covered by dark brown or black chromatophores, typically more concentrated on spine and posterior portion of membrane, forming one or more irregular dark patches, with moderate to relatively large size; patches variably diffuse. Caudal fin with dark brown or black chromatophores, conspicuously more concentrated on rays, variably forming small- to moderate-sized blotches, typically longitudinally elongated (“dash-like”) and diffuse; blotches roughly transversally aligned in some specimens, forming transversal dark stripes; middle portion of caudal-fin base with small irregular dark brown or black dot, variably diffuse or indistinct from mid-dorsolateral stripe; small platelets covering base of caudal-fin rays with conspicuous concentration of dark brown or black chromatophores, variably more concentrated on posterior portion of plates.
Color in life. Similar to color pattern of preserved specimens, but with brighter ground color of body. Wild-caught specimens typically with light brownish orange coloration (Fig. 28); aquarium specimens often with pale brownish yellow or beige coloration (Figs. 29, 30). Additionally, adult aquarium specimens variably with transversal dark stripe on posterior portion of caudal peduncle, just anterior to dark dot on middle portion of caudal-fin base, typical of specimens in early development (see Remarks section below) (Figs. 29, 30); similar pattern on caudal peduncle in one paratype (MNRJ 55758, 46.9 mm SL; Fig. 28). Body covered by greenish yellow iridescent coloration, especially on region of opercle and cleithrum.
Sexual dimorphism. Male specimens of H. tenebrosum present a genital papilla, which is somewhat tubular, a condition well-documented in Corydoradinae (see Britto, 2003; Nijssen, Isbrücker, 1980b; Spadella et al., 2017). The presence of elongated dorsal-fin spine plus two first dorsal-fin branched rays have been associated with dimorphic males of Hoplisoma (see Britto, Lima, 2003; Knaack, 2007; Tencatt et al., 2014a), a feature observed in some specimens of H. tenebrosum. Nonetheless, it was not possible to undoubtedly assign it as a sexually dimorphic feature as most large-sized specimens (fully-developed adults with up to about 50.0 mm SL) with well-developed tubular genital papilla (allegedly males) do not have clearly elongated first branched rays, similar to the observed in specimens lacking genital papilla (allegedly females). Among the paratypes, only one specimen (MNRJ 55758, 46.9 mm SL; Fig. 28) has clearly elongated first and second dorsal-fin branched rays, which also presents a tubular genital papilla.
Variation of the color pattern in life in the type-series of Hoplisoma tenebrosum, showing the general color pattern in lateral view of (A) the holotype, MNRJ 55757, 52.5 mm SL, plus the paratypes (B) MNRJ 55758, 46.9 mm SL, (C) CITL 1459, 44.6 mm SL, (D) CITL 1459, 43.2 mm SL, (E) CPUFMT 8620, 35.2 mm SL, (F) CPUFMT 8620, 30.1 mm SL, and (G) CPUFMT 8620, 29.3 mm SL. Specimens (A, B, E–G) from the igarapé Água-branca, and (C) and (D) from the igarapé do Roncador. Photos by WMO.
Geographical distribution.Hoplisoma tenebrosum is so far known from its type-locality, the igarapé Água-branca (= igarapé Ipixuna), and one of its tributaries, the igarapé Palomita, and also from the igarapé do Roncador, all tributaries of the rio Tapajós, rio Amazonas basin, Amazonas State, Brazil (Fig. 15).
Ecological notes. According to local fishermen from Jacareacanga, Pará State (M. Pinheiro, 2023, pers. comm.), H. tenebrosum presents similar behavior and habitat to the described for H. noxium (see Ecological notes section). At the type-locality, the igarapé Água-branca, H. tenebrosum cooccurs with two other Corydoradinae species, Brochis bifasciatus and Hoplisoma sp. CW127, and with B. ornata (Nijssen & Isbrücker 1976) and Hoplisoma sp. C133 in the igarapé do Roncador, forming mimetic trios in these two sites.
Variation of the color pattern in life in uncatalogued and unmeasured aquarium specimens of Hoplisoma tenebrosum recognized in the aquarium trade by the codes CW160 (A–C) and CW168 (D), in lateral view. Photos (A) and (C) by Hans Evers, photo (B) by Ingo Seidel, and (D) by Hans Gruber.
Etymology. The specific epithet “tenebrosum” derives from the Latin noun “tenebrae”, which means “darkness, gloom”, plus “-ōsum”, a Latin suffix used to form adjectives from nouns. In Brazil, the adjective tenebrous is often used to describe something that is frightening, gloomy, or malevolent. The name alludes to the powerful toxin released by the new species under stress, which kills any fish kept in the same bag/container during transport. An adjective.
Conservation status. Currently, the new species is known only from its type-locality, the igarapé Água-branca, and a single additional record in the igarapé do Roncador, both tributaries of the rio Tapajós in Amazonas State, Brazil. Despite the relatively restricted geographical distribution, the region where both streams flow is protected by Conservation Units, such as the Floresta Nacional de Urupadi and Parque Nacional do Acari, as well as by indigenous territories. Therefore, considering the currently available data and according to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN Standards and Petitions Subcommittee, 2022), Hoplisoma tenebrosum would be classified as Least Concern (LC).
Breeding pair, with (A) the male and (B) the female, plus an ontogenetic series of Hoplisoma tenebrosum (bred under aquarium conditions), showing general changes in external morphology and color pattern in specimens with (C) 12.0 mm TL, (D) 18.0 mm TL, and (E) 28.0 mm TL. Photos by Hans Evers.
Remarks. Currently, the new species is known to occur in three localities, the igarapé Água-branca (or Ipixuna) and its smaller tributary, the igarapé Palomita, and the igarapé do Roncador, both draining to the rio Tapajós, presenting subtle differences in color pattern in each of them. Specimens from the igarapé Água-branca and igarapé Palomita typically present wider mid-dorsolateral and mid-ventrolateral (Fig. 28), while the specimens from the igarapé do Roncador typically display slender stripes (Fig. 28). Similar to the case involving H. noxium, the syntopic (regarding water body, not mesohabitat) Corydoradinae species with convergent color pattern (i.e., mask-like blotch, anterior portion of dorsal fin and the region surrounding anterior portion of its base dark, plus dark longitudinal stripes on flanks) in each of these sites are taxonomically different. As aforementioned, in the Água-branca/Palomita system, the new species cooccurs with B. bifasciata (CW135) and a putatively undescribed species of Hoplisoma, coded as CW127, both with wide longitudinal dark stripes on flanks, whereas the population of the igarapé do Roncador was found in syntopy with B. ornata (CW134) and a putatively undescribed congener, Hoplisoma sp. C133, both with slender stripes. The snout shape of H. tenebrosum presents a range of variation similar to that described for H. noxium (see Remarks section). Likewise, the snout becomes more pronounced with growth and no differences among different populations were observed (Figs. 28–30).
Hoplisoma tenebrosum has been bred under aquarium conditions by Hans-Georg Evers (Fig. 30), who documented its ontogenetic development from 12.0 to 28.0 mm LT, showing general changes in external morphology and color pattern (Fig. 30). Specimen with 12.0 mm TL in early post-flexion stage (Fig. 30); head slightly depressed, becoming gradually deeper along individual’s growth; snout relatively short and rounded; barbels with relatively well-developed papillae, which will gradually become less developed along individual’s growth; eye moderate in size; median fin fold present, slightly absorbed, extending from posterior margin of dorsal fin to genital opening; all rayed fins with distinct rays, including dorsal- and pectoral-fin spines; dorsal fin almost completely detached from median fold; pelvic fin distinct; anal and caudal fins partially detached from fin fold, with caudal-fin asymmetrical, its dorsal portion slightly longer than ventral; hypural plates visible by transparency; adipose fin indistinct; body plates apparently absent.
Specimen in early post-flexion stage (12.0 mm TL; Fig. 30) with body covered by dark brown or black chromatophores, clearly more evident on head, forming large, smoothly arched dark patch extending from anterior portion of parieto-supraoccipital towards region of interopercle, transversally crossing orbit and forming typical mask-like blotch; oblique dark stripe from anteroventral margin of orbit to upper lip lateral area, which gradually fades along individual’s growth. Flanks with diffuse dark markings; middle portion of caudal-fin base with small irregular dark brown or black dot; diffuse transversal dark stripe on posterior portion of caudal peduncle, just anterior to dark dot on middle portion of caudal-fin base; body covered by greenish yellow iridescent coloration.
Specimen with 18.0 mm TL in early juvenile stage (Fig. 30), with snout slightly more pronounced; median fold almost completely absorbed, with all fins more developed, especially adipose and anal fins; adipose fin almost completely detached from fin fold, with distinct spine; caudal fin smoothly bilobed, connected to adipose fin by small portion of fin fold; body plates visible. Body slightly more pigmented, with conspicuous concentration of dark-brown or black chromatophores, forming longitudinal series of diffuse moderate-sized blotches on flanks, more evident on flank midline; transversal dark stripe on caudal peduncle slightly more evident; caudal fin with somewhat transversal dark stripes. Specimen with 28.0 mm TL in juvenile stage, with fin fold completely absorbed, all fins clearly more developed; caudal-fin ventral lobe more evident; body plates conspicuously more developed but not fully covering flanks; color pattern overall similar to adults, except for mid-ventrolateral dark stripe, which is still not well defined, and the presence of conspicuous transversal dark stripe on caudal peduncle, which is typically absent in adults.
DISCUSSION
In the last decades, the snout shape has been proven to be extremely useful for recognizing species (e.g., Tencatt et al., 2016, 2019, 2022a; Espíndola et al., 2018) and/or species groups and lineages (e.g., Nijssen, Isbrücker, 1980a; Alexandrou et al., 2011; Bono et al., 2019) within Corydoradinae. More recently, aspects related to snout morphology were even used to recognize and delimit the genera of Corydoradinae (see Dias et al., 2024). However, some intrageneric variation was observed, most notably in Brochis, but also in Hoplisoma, with some overlap between the two (Dias et al., 2024). Along with the lateral ethmoid and palatine, one of the bones that most reflects the external appearance of the snout is certainly the mesethmoid. In Callichthyidae, this bone presents a roughly lanceolate shape, with two main portions, the wider posterior half and the pointed anterior half (Fig. 31). In the posterior portion, there are two main bony expansions: (i) the lateral posterodorsal expansion, which typically presents a roughly triangular or trapezoid external projection, and (ii) the ventrolateral expansion (= internal medial process in Vera-Alcaraz (2013)). These expansions, one or the other or both, can be variably extended anteriorly, forming lateral laminar edges along dorsal half of anterior portion of mesethmoid (Fig. 31). Considering the potential homologies hypothesized here, the limit between anterior and posterior portions of mesethmoid seems to be better represented by the ventralmost tip of ventrolateral expansion (Fig. 31).
The mesethmoid was characterized by Britto (2003) as: (1) a short (character 1, state 1; fig. 1B) or long (char. 1, state 0; fig. 1A) anterior tip/process, (2) a narrow (char. 2, state 0; fig. 1A) or wide (char. 2, state 1; fig. 1B) posterior portion, and (3) presence (char. 3, state 0; fig. 2A) or absence (char. 3, state 1; fig. 2B) of the lateral cornua on its anterior tip/process. In his unpublished thesis, Vera-Alcaraz (2013) raised an additional character related to the length of mesethmoid postero-lateral process (p. 25, char. 3), which can be very small or absent (state 0), short (state 1) or long (state 2). Although these characters allow a substantial morphological analysis of the bone itself, the relation between the morphology of the mesethmoid and the snout shape was never properly investigated, as well as its possible implications for relationships within the Corydoradinae.
In light of the new classification proposed by Dias et al. (2024), the complex relationship between mesethmoid and snout shape is reflected in Britto’s (2003) morphological phylogenetic hypothesis. The clade II of Britto (2003:144, fig. 24) is composed by typically long-snouted species, harboring Corydoras and some representatives of Brochis. Other species of Brochis, even some with a conspicuously long snout (e.g., B. multiradiata (Orcés V., 1960)),were found more closely related to some Osteogaster species (p. 144, fig. 24, clade IX), but in a large polytomy including Gastrodermus and Hoplisoma (p. 144, fig. 24, see large clade including polytomy plus clades IV–IX), which typically display a shorter and/or rounder snout. Moreover, some species of Brochis present a shorter snout, such as B. reticulata (Fraser-Brunner, 1938), being coded in state 1 for character 1 in Britto’s (2003) data matrix, i.e., with anterior tip of mesethmoid shorter than 50% of entire bone length. The multiple conditions observed in Brochis makes it clear that a deeper analysis of the snout morphology, including one of its main bones (mesethmoid), is needed to better understand both the systematics (Britto, 2003; Dias et al., 2024) and ecology (Alexandrou et al., 2011) of the Corydoradinae.
Mesethmoid and snout shape variations in Aspidoras, showing the general morphology of the mesethmoid of (A) A. lakoi (MNRJ 5293, 30.0 mm SL) in dorsal (top) and lateral (bottom) views, and of (B) A. velites (MZUSP 73264, 24.4 mm SL) in dorsal view. Head profile on the right side of (A) and (B) showing the general aspect of the snout in their respective species in life, both uncatalogued. Abbreviations: apm: anterior portion of mesethmoid, eplp: external projection of lateral posterodorsal expansion of mesethmoid, lmb: length of mesethmoid base, ppm: posterior portion of mesethmoid, pmm: posterior margin of mesethmoid, pve: ventrolateral expansion of posterior portion of mesethmoid, vle: ventrolateral laminar expansion of anterior portion of mesethmoid. Black arrow in A (bottom) indicates the limits between anterior and posterior portion of mesethmoid. Profile photo in (A) by LFCT, and in (B) by Hans Evers. Scale bars = 1 mm.
In this context, two initially antagonistic premises are implied: (i) the morphology of the mesethmoid, and, as a consequence, the snout shape, is poorly informative in a phylogenetic sense, or (ii) the characters analyzed by Britto (2003) fail to recover the phylogenetic information of this bone. After the analysis of representatives from the seven genera within Corydoradinae, it was possible to refine Britto’s (2003) morphological analysis of the mesethmoid and better understand its implications for the most recent phylogeny of the subfamily (i.e., Dias et al., 2024). Interestingly, it was possible to not only accept premise (i), but also partially accept premise (ii), especially regarding the general external appearance of the snout. As the main result of our analysis, we were able to recognize morphological types of mesethmoid within each genus of Corydoradinae, with interesting insights into the relationship between the morphology of this bone and the general aspect of the snout in lateral view (Figs. 31–37).
In addition to the aforementioned characters available in the literature (Britto, 2003; Vera-Alcaraz, 2003), it was possible to raise six other characters and provide their respective putative character-states (summarized in Tab. 3). As this work does not represent a phylogenetic study, we did not hypothesize the transformation series of the characters raised herein, and, consequently, no polarization was performed. Likewise, no exhaustive codification was done. Therefore, the main objective of our analysis is to describe the different morphological patterns of the mesethmoid in Corydoradinae based on material examined throughout the last 25 years (e.g., Britto, 1998, 2003; Britto, Castro, 2002; Britto, Reis, 2005; Britto et al., 2005, 2007, 2009; Tencatt et al., 2013, 2014a,b, 2016, 2019, 2020, 2021, 2022a,b, 2023a,b, 2024a,b; Tencatt, Pavanelli, 2015; Tencatt, Britto, 2016; Tencatt, Evers, 2016, Tencatt, Ohara, 2016a,b; Espíndola et al., 2018; Bono et al., 2019), highlighting yet poorly- or non-explored features related to this bone, especially those that apparently produce significant external morphological changes. Characters that do not seem to be directly related to the general external aspect of the snout in lateral view were not explored herein, such as the lateral cornua on anterior tip/process of mesethmoid (Britto, 2003:123, char. 3; Vera-Alcaraz, 2013:24, char. 0), as well as the length of its postero-lateral process and the exposition of its posterior portion (Vera-Alcaraz, 2013:25–26, chars. 3 and 4, respectively). Similarly, two anatomical structures related to the anterior portion of the mesethmoid, more specifically its ventrolateral laminar expansion and the lateral laminar edges along its dorsal half, both apparently not previously mentioned in the literature, were illustrated but not further discussed.
Characters related to the mesethmoid and their respective putative character-states (not polarized), all raised herein. Abbreviations: eplp: external projection of lateral posterodorsal expansion of mesethmoid, vle: ventrolateral laminar expansion of anterior portion of mesethmoid.
In our analysis, Britto’s (2003) character 1 (i.e., size of mesethmoid anterior portion) was treated exactly like originally proposed, but using the limits between the anterior and posterior portions established here. Although treated as equivalent by Vera-Alcaraz (2013:25), his character 2 (i.e., width of mesethmoid posterior margin) and Britto’s (2003) character 2 (i.e., width of mesethmoid posterior portion) are interpreted herein as distinct, as the latter considered the whole posterior portion/half of the mesethmoid (including whole lateral posterodorsal expansion; see p.123) to establish the width of mesethmoid posterior portion, while the former only considered its posterior margin, along the suture with the frontal bones, to assess this character. Nevertheless, the character 2 in Britto (2003) seems to represent a more generalized interpretation encompassing characters 2 and 3 (i.e., length of mesethmoid postero-lateral process) in Vera-Alcaraz (2013). Therefore, considering that characters 2 and 3 in Vera-Alcaraz (2013) vary independently among the Corydoradinae, we considered his approach as potentially more phylogenetically informative than Britto’s (2003) character 2 for future phylogenetic analysis. Notwithstanding, the postero-lateral process of mesethmoid as described by Vera-Alcaraz (2013:25, char. 3) is named herein as external projection of the lateral posterodorsal expansion of mesethmoid, as this seems a more accurate description of this structure.
As mentioned by Britto (2003) and Vera-Alacaraz (2013), the Loricarioidea typically presents well-developed anterior portion of mesethmoid, which is at least half as long of this entire bone. We observed some minor discrepancies within each of Britto’s two character-states. In the species with short anterior portion of mesethmoid, a condition typically found in groups with clearly short snout, such as Gastrodermus (e.g., G. guapore (Knaack, 1961), G. undulatus (Regan, 1912)) and some Hoplisoma (e.g., H. froehlichi (Tencatt, Britto & Pavanelli, 2016), H. polystictum), this portion is just slightly smaller than half of the total bone length (Figs. 34, 35). In Gastrodermus sp. CW153, an extreme condition was observed, with the anterior portion of mesethmoid being strongly reduced, conspicuously smaller than half of its entire length (Fig. 34D). However, some species with a clearly longer snout also present proportionally short anterior portion of mesethmoid, such as some of the species nested in the subclade composed by B. splendens (Castelnau, 1855) and its closest relatives (see Dias et al., 2024; hereafter the “B. splendens group”) (e.g., B. britskii Nijssen & Isbrücker, 1983, B. cf. splendens) (Fig. 32B).
Considering the limit between the anterior and posterior portions of the mesethmoid established herein, the size of the anterior portion is also reinterpreted as proportionally short in some species of Corydoras (e.g., some specimens of C. caramater, C. iiap Tencatt, Ruiz-Tafur & Chuctaya, 2024, C. zawadzkii Tencatt & Ohara, 2016; see Fig. 33, bottom left) and in some species of Brochis nested in the subclade composed by B. ambiacus (Cope, 1872) and its closest relatives (see Dias et al., 2024; hereafter the “B. ambiacus group”) (e.g., B. arcuata (Elwin, 1938), some specimens of B. brittoi (Tencatt & Ohara, 2016); Fig. 32A), which were previously considered to only present a long anterior portion of mesethmoid (see Tencatt, Ohara, 2016b; Tencatt et al., 2019, 2024a,b). In species with intermediary condition between short and long snouts, it was possible to observe a short or long anterior portion of mesethmoid. The species of Brochis nested in the subclade composed by B. reticulata and its closest relatives (see Dias et al., 2024; hereafter the “B. reticulata group”) present a relatively short anterior portion of mesethmoid (Fig. 32D), whereas specimens of B. difluviatilis (Britto & Castro, 2002) typically display a long anterior portion of mesethmoid (Fig. 32C). Regardless of snout size, which ranges from moderate to relatively long, the anterior portion of mesethmoid is relatively short in both new species (Figs. 4, 21).
Mesethmoid and snout shape variations in Brochis, showing the general morphology of the mesethmoid of (A) B. arcuata (ZUFMS 5724, 47.9 mm SL) in dorsal view, (B) B. britskii (ZUFMS 28, 62.0 mm SL) in dorsal view, (C) B. difluviatilis (DZSJRP 15824, 39.0 mm SL), and (D) B. pantanalensis (CPUFMT 6243, 49.1 mm SL) in dorsal (top) and lateral (bottom right) views. Head profile on the right side of (A) and (C) showing the general aspect of the snout in their respective species in life, and of B. reticulata in (B) and Brochis cf. splendens in (D), all uncatalogued. Abbreviations: eplp: external projection of lateral posterodorsal expansion of mesethmoid, lc: lateral cornua, pve: ventrolateral expansion of posterior portion of mesethmoid. Black arrow in D (bottom right) indicates the limits between anterior and posterior portion of mesethmoid. Profile photos in (A–D) by Hans Evers. Scale bars = 1 mm.
According to Vera-Alcaraz (2013), the width of the posterior margin of the mesethmoid can be narrow (p. 25, char. 2, state 0), smaller than its width at the ventrolateral expansion (named as internal medial process by this author), wide (state 1), equal to its width at the ventrolateral expansion, or extremely wide (state 2), larger than its width at the ventrolateral expansion. Considering that the ventrolateral expansion on the posterior portion of the mesethmoid is difficult or impossible to visualize in dorsal view in most Corydoradinae, especially in Aspidoras, Gastrodermus, Hoplisoma, and Osteogaster, we suggest using the widest region of the posterior portion of the mesethmoid in dorsal view as the main reference to assess this character. This approach makes more sense since, in species where the ventrolateral expansion cannot be seen in dorsal view, such a structure is located just below the external projection of the lateral posterodorsal expansion, which precisely corresponds to the widest region of the posterior portion of mesethmoid. Contrary to Vera-Alcaraz (2013:25, char. 2, state 2), the posterior margin of the mesethmoid in Corydoradinae is, at most, equal in width to the widest region of the posterior portion of mesethmoid. Therefore, we suggest that the character-states should be interpreted as follows: (I) narrow, its width clearly smaller than widest region of the posterior portion, and (II) wide, its width similar to widest region of the posterior portion. Regarding state (I), it was possible to observe that some species may present comparatively narrower posterior margin. It was not possible, however, to clearly delimit a different character-state for these cases, especially when comparing congeners within Aspidoras, Hoplisoma, and Scleromystax.
Other interesting patterns regarding related character were observed. In Gastrodermus, which includes the species with the shortest snout among Corydoradinae, the posterior margin of the mesethmoid is typically wide (Fig. 34A–C), with the exception of Gastrodermus sp. CW153, which presents conspicuously narrow posterior margin (Fig. 34D). Within Aspidoras and Scleromystax, the species with comparatively shorter snout (e.g., most Aspidoras, S. prionotos (Nijssen & Isbrücker, 1980), S. salmacis Britto & Reis, 2005) shares a wider posterior margin of mesethmoid, whereas the species with longer snout (e.g., A. psammatides Britto, Lima & Santos, 2005, A. velites Britto, Lima & Moreira, 2002, S. barbatus (Quoy & Gaimard, 1824)) present a narrower posterior portion (Figs. 31, 37). Among Brochis, the species from the B. reticulata group, which have the shortest snout among congeners, present state 1 for this character (Fig. 32D). In contrast, the long-snouted congeners within the groups B. ambiacus and B. splendens (Fig. 32A, B) share the state 0. In B. difluviatilis, both states were observed. Similar to that observed in the B. ambiacus group, the typical long-snouted species of Corydoras also have a clearly narrow posterior margin of the mesethmoid (Fig. 33). Regarding Hoplisoma and Osteogaster, no conspicuous pattern related to this character and snout shape was observed.
The first character raised herein refers to the overall size of the mesethmoid, including both anterior and posterior portions, which present remarkable variation within the group. To assess this character, we adopted the length of the frontal bone as the main reference instead of the apparently more intuitive head length. The latter is directly affected by the size of the posterior process of the parieto-supraoccipital, which is typically reduced in Aspidoras, making the character not applicable for the species in this genus. Regarding this character, at least three different putative character-states were observed, namely: short, moderate and long. In most Corydoradinae, including both new species, the mesethmoid presents a moderate size, which is larger than half of entire length of frontal, but smaller than its entire length. Interestingly, a moderate-sized mesethmoid was observed in species with diametrically opposite snout morphology, such as G. guapore and H. froehlichi, with conspicuously shorter/rounder snouts (Figs. 34, 35), and B. brittoi and B. cf. splendens, with conspicuously longer/pointed snouts (Fig. 32B). Alternatively, a short mesethmoid, with size up to about half of the frontal’s entire length, was observed in some representatives of Gastrodermus (e.g., G. undulatus). In Corydoras, some Aspidoras (e.g., A. psammatides, A. velites), most species of the B. ambiacus group, some of the species of the B. splendens group (e.g., B. britskii), and some Scleromystax (e.g., S. barbatus, S. lacerdai), the mesethmoid is long, with size equal to or longer than entire length of frontal.
The typical mesethmoid and snout shape in Corydoras, showing the general morphology of the mesethmoid of C. iiap (MNRJ 55393, 50.4 mm SL) in dorsal (top) and lateral (bottom; modified from Tencatt et al. (2024b:8, fig. 2B)) views. Abbreviations: apm: anterior portion of mesethmoid, eplp: external projection of lateral posterodorsal expansion of mesethmoid, ppm: posterior portion of mesethmoid, pve: ventrolateral expansion of posterior portion of mesethmoid, vle: ventrolateral laminar expansion of anterior portion of mesethmoid. Black arrow (bottom left) indicates the limits between anterior and posterior portion of mesethmoid. Head profile on the right refers to the respective species (CIIAP 2649, 52.4 mm SL) in life, taken by Morgan Ruiz-Tafur. Scale bars = 1 mm.
As described by Vera-Alcaraz (2013:25, char. 3), a distinct external projection on the lateral posterodorsal expansion of mesethmoid is typically present in Corydoradinae, although variably reduced (Fig. 33) or even absent (Fig. 32A). Moreover, the general shape and width of its distal portion (parallel to longitudinal body axis) in dorsal and dorsolateral perspectives, respectively (treated herein as two distinct characters), can be conspicuously different within the subfamily. This structure typically has a roughly trapezoid shape (sometimes roughly triangular), being slightly bent posteriorly or roughly laterally straight (transversally set in relation to longitudinal axis of body), articulating to the anterodorsal expansion of the lateral ethmoid (Figs. 4, 21, 31–37). To assess this character, we considered the extension of the area of suture between the external projection and the lateral ethmoid. The Corydoradinaetypically present a relatively narrow, roughly trapezoid external projection on the lateral posterodorsal expansion of the mesethmoid (Figs. 31, 32C, D, 34, 35), with a small area of suture between the external projection and the lateral ethmoid. In some Gastrodermus, such as G. guapore, G. undulatus and G. cf. pygmaeus, this projection can be notably narrow in some specimens (Figs. 34A, B), but it was not possible to recognize such condition as a putative character-state because the difference between it and that described just above is too subtle.
Mesethmoid and snout shape variations in Gastrodermus, showing the general morphology of the mesethmoid of (A) G. guapore (ZUFMS 4000, 29.2 mm SL) in dorsal (top) and lateral views (bottom right), (B) G. cf. pygmaeus (CITL uncatalogued, 22.6 mm SL) in dorsal view, (C) G. undulatus (MZU 1230, 34.5 mm SL) in dorsal view, and (D) Gastrodermus sp. CW153 (CITL uncatalogued, 18.3 mm SL). Head profile on the right side of (A–D) showing the general aspect of the snout in their respective species in life, all uncatalogued. Abbreviations: eplp: external projection of lateral posterodorsal expansion of mesethmoid, lc: lateral cornua, pve: ventrolateral expansion of posterior portion of mesethmoid. Profile photos in (A), (C) and (D) by Hans Evers, in (B) by WMO. Scale bars = 1 mm.
Mesethmoid and snout shape variations in Hoplisoma, showing the general morphology of the mesethmoid of (A) H. polystictum (CITL uncatalogued, 35.8 mm SL), and (B) H. froehlichi (MCP 12945, 38.3 mm SL), both in dorsal view. Head profile on the right side of (A) and (B) showing the general aspect of the snout in their respective species in life, both uncatalogued. Abbreviations: eplp: external projection of lateral posterodorsal expansion of mesethmoid, lc: lateral cornua. Profile photo in (A) by LFCT, in (B) by Hans Evers. Scale bars = 1 mm.
Alternatively, some representatives of Hoplisoma, such as both new species described herein (Figs. 4, 21) plus other morphologically similar congeners (e.g., H. colossus and H. granti), and Scleromystax (e.g., S. prionotos; Fig. 37D) have a relatively wide roughly triangular or trapezoid external projection, with a longer suture between the external projection and the lateral ethmoid. Some species may display intraspecific variation, such as B. difluviatilis and Osteogaster sp. CW68 (Fig. 36), which variably present a narrow or relatively wide roughly triangular or trapezoid external projection. Similarly, Corydoras, some species of the B. ambiacus group, and some Scleromystax (e.g., S. barbatus) can also present a relatively wide roughly triangular or trapezoid external projection, but promptly differ from the condition found in some Hoplisoma and Scleromystax, and variably in B. difluviatilis and Osteogaster sp. CW68, by having longitudinally elongated posterior portion of mesethmoid (Figs. 33, 37A) (vs. posterior portion compact; Figs. 4, 21, 32C, 36, 37D). In species of the “B. splendens group”, the external projection of the lateral posterodorsal expansion of mesethmoid is also wide and roughly trapezoid, but conspicuously expanded anterolaterally, a unique condition among the Corydoradinae (Fig. 32B). Some species within Corydoras and the B. ambiacus group may present strongly reduced external projection (poorly projected laterally), being variably indistinct from the posteriormost portion of mesethmoid, and thus considered as absent (Fig. 32A). Interestingly, the complete absence of this expansion was observed herein to be intraspecifically variable, as in the case of C. caramater.
Another interesting character raised herein refers to the position of the ventrolateral expansion of the mesethmoid, which articulates to the anteroventral expansion of the lateral ethmoid and dorsolateral laminar expansion of the palatine. In most Corydoradinae, including both new species, the ventrolateral expansion of the mesethmoid typically emerges just ventrally or slightly anteroventrally to the lateral posterodorsal expansion of mesethmoid, being partially or not visible in dorsal view (Figs. 4, 21, 31, 32B–D, 34, 35, 36, 37C, D). In these species, the posterior portion of the mesethmoid presents an overall compact shape of similar width and length (Figs. 4, 21, 31, 32B–D, 34, 35, 36, 37C, D). In Corydoras, the species within B. ambiacus group and some Scleromystax (e.g., S. barbatus and S. lacerdai), the ventrolateral expansion of the mesethmoid is easily seen in dorsal view, emerging further anteriorly to the lateral posterodorsal expansion. This gives a longitudinally elongated aspect to mesethmoid’s posterior portion, with its width clearly smaller than length (Figs. 32A, 33, 37A, B).
The typical mesethmoid and snout shape in Osteogaster, showing the general morphology of the mesethmoid of Osteogaster sp. CW68 (MNRJ 55728, 40.9 mm SL mm SL) in dorsal view. Abbreviation: eplp: external projection of lateral posterodorsal expansion of mesethmoid. Head profile on the right refers to the respective species (uncatalogued) in life, taken by WMO. Scale bar = 1 mm.
Our analysis also revealed that the length of the mesethmoid base, which spans the distance between the lateral posteriormost edge of mesethmoid, i.e., at the lateral suture point between the frontal and mesethmoid, and the posterior origin of the external projection of the lateral posterodorsal expansion of mesethmoid (Fig. 31A) can also differ within Corydoradinae. This character could not be assessed in the species lacking the external projection on lateral posterodorsal expansion of mesethmoid, which is the case of some species of Corydoras and the B. ambiacus group (see Fig. 32A). In general, the Corydoradinae have the mesethmoid base length ranging from conspicuously short (Figs. 33, 34C, 37A) to short (Figs. 31A, 32B, D, 34A, 35A, 36). However, a relatively long mesethmoid base was observed in some representatives of Aspidoras (e.g., A. psammatides, A. velites,), Brochis (e.g., B. difluviatilis), Gastrodermus (e.g., G. cf. pygmaeus, Gastrodermus sp. CW153), Hoplisoma (e.g., H. froehlichi, Hoplisoma sp. CW193), Osteogaster (e.g., Osteogaster sp. CW68), and Scleromystax (e.g., S. lacerdai, S. prionotos, S. virgulatus; variable in S. macropterus) (Figs. 31B, 32C, 34B, D, 35B).
Mesethmoid and snout shape variations in Scleromystax, showing the general morphology of the mesethmoid of (A) S. barbatus (UFRJ 4457, unmeasured, disarticulated specimen), (B) S. lacerdai (MNRJ 26017, 36.3 mm SL), (C) S. macropterus (UFRJ 442, unmeasured, disarticulated specimen), and (D) S. prionotos (UFRJ 4431, unmeasured, disarticulated specimen), all in dorsal view. Head profile on the right side of (A–D) showing the general aspect of the snout in their respective species in life, all uncatalogued. Abbreviations: eplp: external projection of lateral posterodorsal expansion of mesethmoid, pve: ventrolateral expansion of posterior portion of mesethmoid, vle: ventrolateral laminar expansion of anterior portion of mesethmoid. Profile photos in (A) and (D) by Hans Evers, in (B) by Mark Smith, and (C) by Rob McLure. Scale bars = 1 mm.
Besides the size of the anterior tip/process of mesethmoid in relation to the entire length of the bone, it was possible to raise a single additional character related to this structure, which refers to its orientation in lateral view. In general, the Corydoradinae possess the anterior tip of the mesethmoid roughly straight, variably inclined (upwards or downwards), but diagonally pointing forward (Figs. 4, 21, 31A, 32D, 33, bottom left). Alternatively, some representatives of Hoplisoma (e.g., H. benattii, H. froehlichi, Hoplisoma sp. CW193) and of Gastrodermus (e.g., G. guapore, Gastrodermus sp. CW153) have the anterior tip of the mesethmoid curved inwards, pointing downward (Fig. 34A, bottom right). Interestingly, in species with curved inwards anterior tip of mesethmoid the snout is not necessarily conspicuously short but markedly round anteriorly (see Fig. 34D).
Based mostly on size, Alexandrou et al. (2011) proposed five types of snout, as follows: extra-long (XL), long (L), intermediate long (IL), intermediate short (IS), and short (S). Considering the new classification by Dias et al. (2024) and the groups of species in Brochis proposed herein, the extra-long snout is present only in species of the B. splendens group, long snout in Corydoras and Scleromystax, intermediate-long snout only in species of the B. ambiacus group, intermediate short only in Gastrodermus, and short snout in Aspidoras and Hoplisoma. Although the analysis of Alexandrou et al. (2011) is mostly accurate in describing the different snout patterns in Corydoradinae, it is important to mention that part of it is imprecise, based on a general resemblance. The species from the B. splendens group indeed possess clearly long snouts, however, we found no conspicuous difference (considering only relative size) between representatives of both B. splendens and B. britskii and some Aspidoras (e.g., A. psammatides and A. velites), most species from the B. ambiacus group, most Corydoras, some Hoplisoma (e.g., some specimens of H. rikbaktsa and of both new species) and some Scleromystax (e.g., S. barbatus) was found. Therefore, we consider these species as belonging to the long (L) category for practical reasons. In the case of B. multiradiata, the snout is typically conspicuously large, being distinct enough from the aforementioned species to maintain the extra-long (XL) category.
In Aspidoras, most species have a moderately-developed snout (not a short snout), with some representatives alternatively presenting a relatively long snout, such as A. psammatides and A. velites (see Tencatt et al., 2022b). Similar to most Aspidoras, some species of Brochis, such as the species of the B. reticulata group, some specimens of B. brittoi and B. difluviatilis, some Corydoras (e.g., some specimens of C. areio and C. aurofrenatus), some Hoplisoma (e.g., H. granti and H. pavanelliae, especially in large-sized specimens, between 45.0–50.0 mm SL, and H. rikbaktsa), some Osteogaster (e.g., O. melanotaenia and O. zygata, despite apparently intraspecifically variable) and some Scleromystax (e.g., S. macropterus, S. reisi and S. salmacis) have a moderately developed snout. Considering that such a snout pattern is intermediary between the short and large patterns, but is visually closer to the large one, we opted to modify the intermediate long (IL) category sensu Alexandrou et al. (2011) to characterize the species/group of species mentioned above. The most evident inconsistency in the analysis of Alexandrou et al. (2011) refers to Gastrodermus, described by the authors as having an intermediate-short snout. However, the species of this genus typically have a conspicuously short and rounded snout (see Dias et al., 2024:22, fig. 23; hereafter XS), even shorter than the typical short snout (S) found in most Hoplisoma. This conspicuously short and rounded snout was also observed in some Hoplisoma species, as H. benattii and H. froehlichi. Thus, it is clear that longer and shorter snouts can be, and generally are, present in representatives of the same genus (Tab. 4). This makes sense with the findings of Alexandrou et al. (2011) who showed that the different types of snouts are closely related with ecological factors (niche partitioning), and do not necessarily reflect the phylogeny of the group.
The direct correlation between snout shape and generic allocation (previously, lineage recognition) is due to the fact that syntopic species of Corydoradinae with convergent color pattern typically form pairs or trios composed of representatives of different genera (see Alexandrou et al., 2011; Tencatt, Ohara, 2016a,b; Tencatt et al., 2019). However, it is not uncommon to find pairs or trios of syntopic congeneric species of Corydoradinae, regardless of whether or not they have a convergent color pattern (e.g., A. aldebaran and A. velites (Tencatt et al., 2022b); H. hypnos, H. thanatos and Hoplisoma sp. CW171(Tencatt et al., 2022a); Hoplisoma cf. apiaka, H. psamathos and Hoplisoma sp. CW171 (Tencatt et al., 2022a); H. polystictum and Hoplisoma sp. CW152 (LFCT, pers. obs.)). In such cases, the species also present different snout morphology, differing from each other in a similar way to that observed for non-congeneric syntopic species (Fig. 38). This reinforces the idea that different snout shapes are more closely related to ecological aspects. Our analysis of the mesethmoid corroborates this, showing that the snout morphology alone is not reliable for predicting generic allocation in Corydoradinae, as each snout type has arisen independently on multiple occasions within the subfamily (Tab. 4).
The clear resemblance between the snouts of A. velites and S. lacerdai (Figs. 31B, 37B), of Corydoras and the species of the B. splendens group (Figs. 32B, 33), and of both new species and the species of the B. ambiacus group (Figs. 4, 21, 32A) seem to be better explained by adaptive convergence, which also likely explains their similarities in color pattern (see Alexandrou et al. (2011)). The same can be said for the short and markedly rounded snout of G. guapore and H. froehlichi (Figs. 34A, 35B). Interestingly, we have also found that non-congeneric species sharing similar snout shape, such as C. iiap, B. arcuata and S. barbatus, also may share similar mesethmoid morphology (Figs. 32A, 33, 37A). As well as for the snout shape, the anatomy of the mesethmoid alone offers little reliability for generic allocation within Corydoradinae. Therefore, we strongly encourage that the generic placement of forthcoming Corydoradinae new species consider the use of combined features (mostly osteological), especially including the serration pattern of both dorsal- and pectoral-fin spines among them, which is extremely informative within the subfamily (see Dias et al., 2024).
Summarized results of the analysis of both snout (size/shape) and mesethmoid morphology within Corydoradinae. IL = intermediate long, L = long, IS = intermediate short, S = short, XL = conspicuously long, XS = conspicuously short. *Not explicitly stated, but likely to be classified as IS, as in the B. reticulata group.
Variation on the snout morphology of three syntopic species of Hoplisoma, showing snout shape in lateral view in living specimens of (A) H. hypnos (INPA 59774, 28.2 mm SL), (B) H. thanatos, INPA 59777, 33.3 mm SL, and (C) Hoplisoma sp. CW171, uncatalogued, unmeasured. Photos by WMO.
Specimens of H. noxium and H. tenebrosum are often attributed to Brochis in the aquarium trade, especially due to its peculiar head shape, with some specimens presenting a long snout (Fig. 17D). Although more common in species of Corydoras and Brochis, a relatively long snout also can be found in representatives of most genera within Corydoradinae, with Gastrodermus as the only exception. Therefore, we refute the allocation of both new species to Brochis based on snout length alone, especially when considering the serration pattern of both dorsal- and pectoral-fin spines (Figs. 7 and 24 vs. Figs. 39A, B). Except for B. difluviatilis, all species within Brochis share the presence of posterior margin of dorsal- and pectoral-fin spines with most serrations retrorse, whereas both new species present the typical pattern of Hoplisoma, with both spines mostly bearing antrorse serrations. The condition found in almost all Brochis (except in B. difluviatilis, which lacks serrations on dorsal spine) is unique as the remaining Corydoradinae with serrated posterior margin of dorsal-fin spine have mostly antrorse serrations (Figs. 7A, 24A). This condition makes Brochis one of the easiest genera to recognize. Even its pectoral-fin spine serration pattern is unique, as, among the species sharing mostly retrorse serrations (i.e., Corydoras, Brochis (except for B. difluviatilis), most Gastrodermus, and Scleromystax), Brochis is the only group to present typically laminar serrations, with a blade-like aspect (Fig. 39B) (vs. conical serrations; Figs. 39C–E).
Although superficially similar, B. difluviatilis, the only Brochis lacking the serration pattern described above, can also be discarded as closely related to both new species by having the following features: (I) posterior margin of the dorsal-fin spine smooth, lacking serrations (vs. bearing serrations), (II) posterior margin of the pectoral-fin spine with serrations restricted to the proximal region of spine (vs. with serrations in almost its entire length), (III) absence of contact between the parieto-supraoccipital and the nuchal plate (vs. such structures directly contacting each other), and (IV) typically long anterior portion of mesethmoid, its size slightly larger than 50% of bone length (vs. relatively short, slightly smaller than 50% of bone length). The presence of a reduced ossified portion of hypobranchial 2, with size conspicuously smaller than the cartilaginous portion (vs. ossified portion well developed, its size about twice the cartilaginous portion in both new species), is also reported for B. difluviatilis, but considering that a well-developed ossified portion of hypobrancial 2 was observed in some of its representatives, such a feature is unreliably diagnostic.
As mentioned by Dias et al. (2024), two additional species superficially similar to B. difluviatilis were provisionally allocated in Brochis until further analysis, B. costai (Ottoni, Barbosa & Katz, 2016) and B. garbei (Ihering, 1911). This decision was influenced by the results of Alexandrou et al. (2011), who found B. difluviatilis and B garbei closely related, as the voucher specimen(s) of the latter could not be examined at the time. Preliminary results of an ongoing revisionary study of the three aforementioned species by LFCT shows that the morphology of B. garbei matches Hoplisoma instead of Brochis. Considering the high number of B. difluviatilis specimens misidentified as B. garbei (and vice versa) in museums, and the fact that the first potentially represents a species complex due to its highly variable morphology and color pattern (LFCT, pers. obs.), it is reasonable to consider that the species attributed to B. garbei likely represents one of the many morphotypes of B. difluviatilis. As for B. costai, preliminary results showed that its type-series is composed of specimens of both B. difluviatilis and B. garbei, with the holotype fitting the latter in both morphology and color pattern (i.e., body robust, small dorsal- and pectoral-fin spines, conspicuously rounded dark blotches along flank midline, large dark patch on dorsal fin, infraorbital 1 with ventral laminar expansion well developed, and infraorbital 2 in contact with pterotic-extrascapular). However, considering that these results are still unpublished, the taxonomic status of these species remains as proposed by Dias et al. (2024).
Serration pattern on posterior margin of spines in some Corydoradinae genera, showing the typical serration pattern of the (A) dorsal- and (B) pectoral-fin spines of B. arcuata (ZUFMS 5724, 47.9 mm SL), and of the pectoral-fin spines of (C) C. iiap (MNRJ 55393, 50.4 mm SL), (D) G. guapore (ZUFMS 4000, 28.8 mm SL), and (E) S. barbatus (UFRJ 4457, unmeasured, disarticulated specimen). Area where the illustrated bones are located in fish’s body marked in red in the miniature photos (right side) of the respective species in life. Specimen on the right side of (B) under voucher CIIAP 2649, 52.4 mm SL, on the right side of (A), (C) and (D) uncatalogued (aquarium specimens). Photo on the right side of (A) and (B) by SG, (C) by Morgan Ruiz-Tafur, (D) by Markos Alexandrou, and (E) by Hans Evers. Scale bars = 1 mm.
Three features suggest the allocation of both new species to Brochis: (I) the presence of a relatively long and straight snout, variably with a smooth concavity on anterior portion of mesethmoid, in some specimens, (II) infraorbital 1 with ventral laminar expansion typically ranging from well-developed to strongly well developed, and (III) infraorbital 2 contacting pterotic-extrascapular. All of these features, however, are also present in Hoplisoma. Feature (I), a long and somewhat straight snout (IL category), is also present in H. granti, H. pavanelliae, H. rikbaktsa,and Hoplisoma sp. CW171, whereas feature (II) can be observed in H. coppenamense (Nijssen, 1970), H. gossei (Nijssen, 1972), H. lymnades (Tencatt, Vera-Alcaraz, Britto & Pavanelli, 2013) and H. thanatos, and feature (III) in H. eversi and H. granti, and variably in species like H. araguaiaense and H. polystictum. Considering that all features that could potentially indicate a close relationship between the two new species and B. difluviatilis are also present in Hoplisoma, allied to the features previously discussed, especially regarding the serration pattern of both dorsal- and pectoral-fin spines, the two new species are reasonably allocated to Hoplisoma.
One of the most peculiar features in both new species of Hoplisoma is the presence of rounded, elliptical or vermiculated/irregular whitish to brownish yellow or pale yellow/beige blotches on body. Besides H. tenebrosum, the only congeners sharing the presence of pale blotches on body are H. gossei and the species currently recognized as H. sterbai (Knaack, 1962), plus two species of Brochis, B. pinheiroi (Dinkelmeyer, 1995) and B. seussi (Dinkelmeyer, 1996). Considering color pattern alone, both new species can be distinguished from the aforementioned species by having a dark mask-like blotch (vs. mask-like blotch absent).The pattern of dark markings on flanks promptly distinguishes both new species from each other, with H. noxium presenting dark blotches and H. tenebrosum the dark longitudinal stripes (see Color in alcohol sections for both new species).
The color patterns of Corydoradinae species have been used for many years to assist in the diagnosis and differentiation of species, which has sometimes included consideration of the juvenile color pattern (Nijssen, Isbrücker, 1986:40). Fuller (2012) provided evidence of the color change in juveniles for numerous species as they grow into the adult color pattern. Recently, the descriptions of several species have documented color pattern changes from early stages of development to adult (Tencatt, Evers, 2016; Tencatt et al., 2019, 2021, 2023a). The multifunctional nature of adult Corydoradinae color patterns have also received recent consideration (Bentley et al., 2021; Tencatt et al., 2023b), and includes crypsis, aposematism, and a variety of other intraspecific, infraspecific, and intrasexual signaling. As aforementioned, the color pattern of adult H. noxium is an unusual one among Corydoradinae, having a combination of ground color of body brownish yellow to pale yellow or beige, dark mask-like blotch, and both whitish to brownish yellow or pale yellow/beige and dark brown or black blotches on body. The dark markings on the flanks of H. noxium are relatively variable in size, number and distribution pattern/organization (see color pattern accounts for this species; Figs. 1, 11–14). This color pattern was considered “primitive” by Chihiro Yamamoto, one of the discoverers of H. noxium (coded as “Corydoras sp. CW004”) for the aquarium trade, who coined the widely known trade name “Ancestor” (O. Lucanus, 2023, pers. comm.). As previously discussed, the variation in both color pattern and snout shape/length led to the recognition of the different code numbers in the aquarium hobby, i.e., CW004, CW155, CW156, CW167, and, potentially, CW170 (see Introduction; Grant, 2019). The color pattern of H. tenebrosum is somewhat similar to that of H. noxium, but clearly differs by the presence of solid dark brown or black longitudinal stripes instead of the dark speckled pattern on flanks, typically with fewer pale spots on the body (compare Figs. 1 and 19).
The variation in the degree of dark markings in H. noxium can be explained by the reaction–diffusion model (Turing, 1952; Kondo, Asai, 1995; Asai et al., 1999) which may be driven by gene mutation (Watanabe et al., 2006); Fisherian sexual selection amplifying initially small differences in genetic variation between populations (Maan, Sefc, 2013); polychromatism due to frequency-dependent predation (Endler, 1988; Olendorf et al., 2006); and potentially phenotypic plasticity (Nilsson et al., 1995; Prada et al., 2008; Hamel et al., 2020; Lofeu et al., 2021), the latter also potentially being responsible for the differences in snout length. Interestingly, even though presenting similar variation range in dark markings on body and snout length/shape, both features tend to be more conservative in H. tenebrosum, despite occurring in the same basin and area (albeit from different tributaries) and similar biotope and lifestyle. This potentially rules out ecomorphological drivers (Jacquemin, Pyron, 2016).
The general color pattern of H. noxium is reminiscent of some juvenile color patterns of numerous Corydoradinae species (see Tencatt, Evers, 2016; Tencatt et al., 2019; 2023a,b), which usually consist of a brownish to tan body ground color with dark eye mask, and dark spots or blotches on trunk, as well as at the base of the dorsal-fin spine and along the ridge of the back. Changes in color and pattern as fish grow are well documented and have been called Ontogenetic Color Change (Booth, 1990) and covered by the term Morphological Color Change (Leclercq et al., 2010). Juvenile and adult color patterns can differ to the point where the two age groups are erroneously described as different species or genera (see Pearson, 1924:9; Randall, 1996). There are several hypotheses for different color patterns in juveniles compared to adults (Mahon, 1998), such as the reduction of aggression from conspecific adults (Fricke, 1980), although other studies did not support this (Neal, 1993), or even crypsis. As discussed in Bentley et al. (2021), crypsis in Corydoradinae is well documented, but the advantages of a different color pattern in a juvenile have not been discussed for the subfamily.
The visibility of a fish’s color pattern is not just affected by the pattern itself, but by different factors such as the perspective of the observer, the visual background (e.g., substrate) or medium (e.g., water clarity or depth), the visual capabilities of the observer (e.g., color acuity), distance between signaling and observer, ambient lighting, and the behavior of the signaler (Endler, 1978; Tencatt et al., 2023b). In some species, juveniles may inhabit different substrates, or water types/depths than adults. Their size and/or daily movements may play a role in how conspicuous they are. Based on the types of predators they are exposed to, the need to display aposematic coloration or behaviors may also be different for juveniles, as well as any benefit to mimic other species, or the need for infraspecific or infrasexual signaling (Booth, 1990). Biological and ecological factors are also at play such as how colors and patterns develop in immature fishes (Nüsslein-Volhard, Singh, 2017), and the potential lack of consumption of biological pigments that can alter color and pattern (Booth, 1990). The similarity in color pattern of juvenile and adult H. noxium to that of the general juvenile pattern for Corydoradinae would suggests a cryptic function.
Whilst there is some variability in the pattern in H. noxium (as discussed above), putative aposematic color signaling is somewhat reduced in this species. Such color signaling includes iridescence around and directed towards the dorsal- and pectoral-fin spines as well as around the lateral portion of the cleithrum; contrasting banding patterns on the fins or the body; bright colors in fins, particularly on spines, that stand out in stark contrast; and dark colors on fins (Grant, 2022; Tencatt et al., 2023b). However, individuals freshly caught in the field typically exhibit bright pale blotches, greenish yellow iridescent coloration, especially on region of opercle and cleithrum, and an orange tinge all over the body, which suggests some aposematic signaling. The mottled body with a general color and pattern that is reminiscent of their substrate, dark saddles, as well as a dark eye mask, are typical of cryptic color patterning (Cott, 1940; Armbruster, Page, 1996; Bentley et al., 2021; Tencatt et al., 2023b) and diurnal camouflage of benthic but nocturnally active species is known in fishes (Sazima et al., 2006). This apparently enhanced cryptic and reduced aposematic color pattern, with phenotypic color plasticity or polychromatism is perhaps explained by the very unusual behavior of H. noxium.
Hoplisoma noxium and H. tenebrosum were not observed or captured diurnally in their natural habitat, being exclusively captured, in relatively high numbers, at night, as witnessed by LFCT and WMO. This is unusual for a non-troglobitic corydoradine. Our observation in-situ is backed up by aquarists’ anecdotal observations of H. noxium in aquaria; Wild caught adult specimens of CW004 (Mike Zajac, 2023; E. Ball, 2023, pers. comm.), CW155 (Paul Belanger, 2023; Roland van Ouwerkerk, 2023; M. Ortiz, 2023, pers. comm.), CW156 (J. Janisch, 2023, pers. comm.), and also CW170 (M. Rushmore, 2023, pers. comm.), which is rumored to come from a different location to the other codes, herein treated as variable forms of H. noxium, generally hide during light hours, sometimes only moving if they cannot see their keeper. If they notice outside movements, they become startled very easily. Similarly, some F1 juvenile specimens of CW004 and CW155 were reported to be somewhat more active during the day/light than wild adults, whereas both adult and juvenile CW170 have been recorded as active in darkness. Adult wild caught CW004, CW155 and CW170 were reported to only have spawned during the night/in darkness, which is unusual for a corydoradine. Notwithstanding, some F1 specimens of CW004 were reported to spawn in the day/light, while some wild caught CW156 spawned both day and night. Nonetheless, it is important to highlight that the species were not observed foraging at night in their natural habitat, but rather stationary along the banks of the sampled streams. Thus, it is possible that they forage during the day in deeper areas and move to shallow, marginal areas only at night (LFCT and WMO, pers. obs.).
Nocturnality would explain the enhanced cryptic and reduced aposematic color pattern (less reduced in H. tenebrosum), as such patterns would provide an advantage for remaining still (or predominantly so) during diurnal hours. Enhanced aposematic signaling would not be advantageous during nocturnal movements, when lunar or sidereal light limits predators’ optical hunting techniques, and other methods must be utilized (Pohlmann et al., 2001). Some predators tend to be more active in daylight, like some piscivorous birds (Nilsson, 1970; Beckmann et al., 2006). Whilst not apparently overtly aposematic in color pattern, H. noxium and H. tenebrosum are defended by their strong and serrated dorsal- and pectoral-fin spines (i.e., the defensive tripod sensu, Fine, Ladich, 2003), and by releasing a powerful toxin under stress, with local fishermen reporting serious injuries. Many species that can be considered defended display weak warning signals (i.e., are not conspicuously aposematic) and appear cryptic, which can be partly a result of predator presence and behavior (Endler, Mappes, 2004). However, as discussed, both species also have some putative aposematic coloration and this could be of use when specimens encounter predators during daylight hours. As discussed in Bentley et al. (2021), some species are known to have both cryptic and aposematic signals, which can be switched signaled depending on the type of and proximity of interaction between the signaler and the predator.
Comparative material examined.Aspidoras: same as listed in Tencatt et al. (2022b). Brochis: Brochis ambiacus: ANSP 8291, holotype of Corydoras ambiacus Cope, 1872, 40.4 mm SL; MZUSP 26053, 2, 41.8–47.2 mm SL. Brochis approuaguensis: MZUSP 27895-6, 2, 43.0–46.1 mm SL, paratypes of C. approuaguensis Nijssen & Isbrücker, 1983. Brochis arcuata: BMNH 1939.3.3.1, holotype of Corydoras arcuatus Elwin, 1938, 43.3 mm SL. Brochis bethanae: MUSM 69403, holotype of Corydoras bethanae Bentley, Grant & Tencatt, 2021, 51.2 mm SL. Brochis bifasciata: MZUSP 38976, 16, 23.6–30.0 mm SL, paratypes of Corydoras bifasciatus Nijssen, 1972. Brochis britskii: ZUFMS-PIS 862, 12, 72.0–78.0 mm SL. Brochis brittoi: MNRJ 43316, holotype of Corydoras brittoi Tencatt & Ohara, 2016, 38.1 mm SL. Brochis condiscipulus: MZUSP 38957, 7, 34.1–40.3 mm SL, paratypes of Corydoras condiscipulus Nijssen & Isbrücker, 1980. Brochis crimmeni: MZUSP 52490, holotype of Corydoras crimmeni Grant, 1997, 36.1 mm SL. Brochis difluviatilis: MZUSP 75268, holotype of Corydoras difluviatilis Britto & Castro, 2002, 39.8 mm SL. Brochis ephippifer: MZUSP 31605, 2, 44.9–49.1 mm SL. Brochis garbei: MNRJ 18089, 14, 19.2–25.3 mm SL, 2 c&s, 25.9–27.4 mm SL. Brochis heteromorphus: USNM 204224, 2, 37.0–42.7 mm SL, paratypes of Corydoras heteromorphus Nijssen, 1970. Brochis incolicana: MZUSP 45717, holotype of Corydoras incolicana Burgess, 1993, 47.6 mm SL. Brochis leopardus: USNM 93305, lectotype of Corydoras leopardus Myers, 1933, 38.7 mm SL. Brochis ornata: USNM 216075, 1, 37.8 mm SL, paratype of Corydoras ornatus Nijssen & Isbrücker, 1976. Brochis orphnopterus: USNM 204361, holotype of Corydoras orphnopterus Weitzman & Nijssen, 1970, 55.9 mm SL. Brochis pantanalensis: NUP 10188, 1 c&s, 46.4 mm SL; NUP 12593, 21, 38.7–51.2 mm SL. Brochis pinheiroi: MZUSP 48099, holotype of Corydoras pinheiroi Dinkelmeyer, 1995, 54.3 mm SL. Brochis robineae: MZUSP 27175, holotype of Corydoras robineae Burgess, 1983, 33.7 mm SL. Brochis seussi: MZUSP 49323, 10, 44.3–54.0 mm SL, paratypes of Corydoras seussi Dinkelmeyer, 1996. Brochis splendens: NUP 12990, 1, 43.7 mm SL; NUP 10195, 1 c&s, 54.6 mm SL. Brochis virginiae: USNM 326186, 3, 31.6–33.5 mm SL, paratypes of Corydoras virginiae Burgess, 1993. Corydoras: Corydoras acutus: ANSP 113928, 1, 43.0 mm SL; MNRJ 3985, 2, 47.1–54.8 mm SL; USNM 305324,10, 13.6–40.8 mm SL. Corydoras amapaensis: USNM 205865, 1, 46.0 mm SL, paratype of Corydoras amapaensis Nijssen, 1972. Corydoras areio: ZUFMS 1314, 15, 34.4–41.9 mm SL, 2 c&s, 38.1–38.7 mm SL. Corydoras aurofrenatus: NUP 16191, 33, 20.1–53.8 mm SL, 2 c&s, 38.2–41.6 mm SL. Corydoras blochi: MZUSP 8580, 3, 31.0–42.6 mm SL, paratypes of Corydoras blochi Nijssen, 1971. Corydoras caramater: MNRJ 54621, holotype of Corydoras caramater Tencatt, Couto, Santos & Sousa, 2024, 49.3 mm SL; CITL 929, 5 of 6, 35.7–45.3 mm SL, 1 of 6 c&s, 45.3 mm SL, paratypes of Corydoras caramater Tencatt, Couto, Santos & Sousa, 2024. Corydoras coriatae: USNM 343866, 2, 53.2–57.1 mm SL, paratypes of Corydoras coriatae Burgess, 1997. Corydoras desana: ANSP 200804, 2, 29.5–43.4 mm SL, paratypes of Corydoras desana Lima & Sazima, 2017. Corydoras filamentosus: USNM 225536, holotype of Corydoras filamentosus Nijssen & Isbrücker, 1983, 30.2 mm SL. Corydoras fowleri: LBP 12462, 9, 44.3–59.9 mm SL, 1 c&s, 50.4 mm SL. Corydoras fulleri: MUSM 69317, holotype of Corydoras fulleri Tencatt, Santos, Evers & Britto, 2021, 55.1 mm SL. Corydoras geoffroy: USNM 204222, 2, 54.5–55.4 mm SL, paratypes of Corydoras octocirrus Nijssen, 1970. Corydoras iiap: CIIAP 3906, holotype of Corydoras iiap Tencatt, Ruiz-Tafur, Chuctaya, 2024, 55.2 mm SL; MNRJ 55393, 5 of 7, 28.0–50.4 mm SL, 2 c&s of 7, 41.5–50.4 mm SL, paratypes of Corydoras iiap Tencatt, Ruiz-Tafur, Chuctaya, 2024. Corydoras maculifer: NUP 8970, 2, 42.0–46.0 mm SL. Corydoras ourastigma: MZUSP 38950, 1, 23.0 mm SL, paratype of Corydoras ourastigma Nijssen, 1972. Corydoras pastazensis: USNM 177216, holotype of Corydoras pastazensis Weitzman, 1963, 46.2 mm SL. Corydoras sarareensis: MZUSP 48100, holotype of Corydoras sarareensis Dinkelmeyer, 1995, 40.9 mm SL. Corydoras septentrionalis: USNM 130634, 1, 42.3 mm SL, paratype of Corydoras septentrionalis Gosline, 1940; ZMA 112.288, 2, 37.8–46.3 mm SL, paratypes. Corydoras simulatus: USNM 197615, holotype of Corydoras simulatus Weitzman & Nijssen, 1970, 49.1 mm SL. Corydoras spilurus: BMNH 1926.3.2.738, lectotype of Corydoras spilurus Norman, 1926, 43.3 mm SL. Corydoras stenocephalus: MNRJ 3625, 3, 31.2–62.3 mm SL. Corydoras treitlii: NUP 16224, 3, 21.5–45.6 mm SL. Corydoras zawadzkii: MNRJ 45565, holotype of Corydoras zawadzkii Tencatt & Ohara, 2016, 48.7 mm SL; NUP 17824, 1 c&s, 39.9 mm SL, paratype. Gastrodermus: Gastrodermus elegans: USNM 216716, 10, 36.3–43.3 mm SL, paralectotypes of Corydoras elegans Steindachner, 1876. Gastrodermus gracilis: USNM 216074, 1, 19.2 mm SL, paratype of Corydoras gracilis Nijssen & Isbrücker, 1976. Gastrodermus guapore Knaack, 1961: ZUFMS-PIS 4000, 5, 26.9–33.6 mm SL, 2 c&s, 28.8–29.2 mm SL. Gastrodermus hastatus: NUP 6862, 116, 13.1–20.7 mm SL. Gastrodermus napoensis: USNM 270358, 2, 26.7–28.3 mm SL, paratypes of Corydoras napoensis Nijssen & Isbrücker, 1986. Gastrodermus pygmaeus: ANSP 200357, 1, 16.1 mm SL. Gastrodermus cf. pygmaeus: CITL uncatalogued, 38 of 40, 11.4–22.7 mm SL, 2 c&s of 40, 17.5–22.6 mm SL. Gastrodermus undulatus: BMNH 1912.7.10.5, holotype of Corydoras undulatus Regan, 1912, 41.8 mm SL. Gastrodermus sp. CW153: CITL uncatalogued, 22 of 26, 17.3–26.3 mm SL, 4 c&s of 26, 17.0–18.7 mm SL. Hoplisoma: Hoplisoma adolfoi: MZUSP 26641, holotype of Corydoras adolfoi Burgess, 1982, 32.5 mm SL. Hoplisoma amphibelum: ANSP 8290, holotype of Corydoras amphibelus Cope, 1872, 26.4 mm SL. Hoplisoma araguaiaense: MZUSP 87155, 33 4, 24.9–46.7 mm SL, 2 c&s, 27.6–31.8 mm SL. Hoplisoma armatum: BMNH 1867.6.13.51, lectotype of Callichthys armatus Günther, 1868, 42.1 mm SL. Hoplisoma atropersonatum: USNM 204359, holotype of Corydoras atropersonatus Weitzman, Nijssen, 1970, 37.1 mm SL. Hoplisoma benattii: MZUSP 121671, holotype of Corydoras benattii Espíndola, Tencatt, Pupo, Villa‐Verde & Britto, 2018, 25.4 mm SL. Hoplisoma boehlkei: ANSP 148097, holotype of Corydoras boehlkei Nijssen, Isbrücker, 1982, 23.6 mm SL. Hoplisoma bondi: ROM 66202, 134 7, 33.8–39.9 mm SL, 3 c&s, 36.7–38.6 mm SL. Hoplisoma brevirostre: LBP 3080, 10, 23.8–27.7 mm SL, 3 c&s, 25.8–27.9 mm SL. Hoplisoma burgessi: USNM 288461, 2, 43.7–44.8 mm SL, paratypes of Corydoras burgessi Axelrod, 1987. Hoplisoma carlae: NUP 711, 1, 47.9 mm SL; NUP 4425, 1 c&s, 45.0 mm SL. Hoplisoma colossus: MNRJ 54421, holotype of Corydoras colossus Tencatt, Grant & Bentley, 2023, 44.5 mm SL; CITL 928, 1 of 3, 42.2 mm SL, 2 c&s of 3, 43.1–48.4 mm SL, paratypes of Corydoras colossus Tencatt, Grant & Bentley, 2023. Hoplisoma coppenamense: USNM 202129, 5, 33.0–35.8 mm SL, paratypes of Corydoras coppenamensis Nijssen, 1970. Hoplisoma davidsandsi Black, 1987: MZUSP 110066, 40 4, 36.0–41.9 mm SL, 2 c&s specimens, 40.9–42.1 mm SL. Hoplisoma diphyes: ANSP 169756, 2, 40.7–43.1 mm SL. Hoplisoma ehrhardti: NUP 11255, 15, 36.5–46.8 mm SL. Hoplisoma eversi: MNRJ 43195, holotype of Corydoras eversi Tencatt & Britto, 2016, 44.5 mm SL. Hoplisoma flaveolum: MZUSP 424, holotype of Corydoras flaveolus Ihering, 1911, 33.4 mm SL. Hoplisoma gossei: MZUSP 38977, 6, 48.4–53.4 mm SL, paratypes of Corydoras gossei Nijssen, 1972. Hoplisoma granti: MNRJ 51193, holotype of Corydoras granti Tencatt, Lima & Britto, 2019, 48.4 mm SL. Hoplisoma griseum: MZUSP 108896, 13, 4, 31.5–36.2 mm SL, 2 c&s, 30.6–34.5 mm SL. Hoplisoma gryphus: MNRJ 40770, holotype of Corydoras gryphus Tencatt, Britto & Pavanelli, 2014, 32.3 mm SL; NUP 14676, 3 c&s, 27.7–32.4 mm SL, paratypes. Hoplisoma guianense: USNM 204218, 2, 26.0–32.0 mm SL, paratypes of Corydoras guianensis Nijssen, 1970. Hoplisoma hypnos: MNRJ 53288, holotype of Corydoras hypnos Tencatt, Ohara, Sousa & Britto, 2022, 31.7 mm SL. Hoplisoma julii: NUP 16225, 1, 46.8 mm SL. Hoplisoma kanei: MZUSP 52489, holotype of Corydoras kanei Grant, 1997, 36.6 mm SL. Hoplisoma knaacki: MUSM 52730, holotype of Corydoras knaacki Tencatt & Evers, 2016, 35.6 mm SL. Hoplisoma lacrimostigmata: MNRJ 40725, holotype of Corydoras lacrimostigmata Tencatt, Britto & Pavanelli, 2014, 31.8 mm SL; NUP 14657, 3 c&s, 30.9–34.5 mm SL, paratypes. Hoplisoma longipinne: AI 221, holotype of Corydoras longipinnis Knaack, 2007, 59.5 mm SL; NUP 14440, 2 c&s, 29.9–33.4 mm SL. Hoplisoma loretoense: ANSP 121620, 32, 17.3–32.7 mm SL, paratypes of Corydoras loretoensis Nijssen, Isbrücker, 1986. Hoplisoma loxozonum: ANSP 150170, holotype of Corydoras loxozonus Nijssen, Isbrücker, 1983, 34.6 mm SL. Hoplisoma lymnades: MNRJ 15765, 6, 15.8–17.7 mm SL, 2 c&s, 18.1–18.4 mm SL; MNRJ 40186, holotype of Corydoras lymnades Tencatt, Vera-Alcaraz, Britto & Pavanelli, 2013, 29.7 mm SL. Hoplisoma melanistium: BMNH 1864.1.21.86, lectotype of Corydoras melanistius Regan, 1912, 35.0 mm SL. Hoplisoma micracanthus: BMNH 1897.1.27.8, lectotype of Corydoras micracanthus Regan, 1912, 33.7 mm SL. Hoplisoma multimaculatum: MCP 29025, 2, 20.1–25.4 mm SL. Hoplisoma nattereri: MZUSP 110255, 31 4, 32.0–32.8 mm SL, 2 c&s, 32.3–34.4 mm SL. Hoplisoma oiapoquense: USNM 205868, 2, 25.9–35.0 mm SL, paratypes of Corydoras oiapoquensis Nijssen, 1972. Hoplisoma osteocarus: USNM 157367, 1, 25.1 mm SL, paratype of Corydoras osteocarus Böhlke, 1951. Hoplisoma paleatum: BMNH 1917.7.14.18, lectotype of Callichthys paleatus Jenyns, 1842, 30.0 mm SL; NRM 54230, 1, 53.5 mm SL. Hoplisoma panda: BMNH 1969.7.15.8, holotype of Corydoras panda Nijssen & Isbrücker, 1971, 38.9 mm SL; ROM 55815, 6, 26.5–39.7 mm SL. Hoplisoma parallelum: MZUSP 45716, holotype of Corydoras parallelus Burgess, 1993, 47.4 mm SL. Hoplisoma pavanelliae: MNRJ 43317, holotype of Corydoras pavanelliae Tencatt & Ohara, 2016, 45.1 mm SL. Hoplisoma polystictum: BMNH 1895.5.17.62, lectotype of Corydoras polystictus Regan 1912, 27.5 mm SL; CITL uncatalogued, 3 c&s, 30.7–35.8 mm SL. Hoplisoma psamathos: MNRJ 53289, holotype of Corydoras psamathos Tencatt, Ohara, Sousa & Britto, 2022, 29.4 mm SL. Hoplisoma potaroense: ROM 61526, 3 of 15, 35.0–44.8 mm SL, 2 c&s, 32.6–35.1 mm SL. Hoplisoma punctatum: ZMB 3149, lectotype of Cataphractus punctatus Bloch, 1794, 41.7 mm SL. Hoplisoma simile: LBP 10648, 7, 21.4–34.3 mm SL. Hoplisoma surinamense: USNM 204223, 2, 29.1–34.3 mm SL, paratypes of Corydoras surinamensis Nijssen, 1970. Hoplisoma thanatos: MNRJ 53287, holotype of Corydoras thanatos Tencatt, Ohara, Sousa & Britto, 2022, 33.2 mm SL. Hoplisoma trilineatum: ANSP 8294, lectotype of Corydoras trilineatus Cope, 1872, 31.8 mm SL; MZUSP 30857, 25, 3, 40.9–44.1 mm SL, 2 c&s, 44.2–43.8 mm SL. Hoplisoma tukano: MZUSP 82100, holotype of Corydoras tukano Britto & Lima, 2003, 40.9 mm SL. Hoplisoma urucu: MNRJ 32446, 4, 25.9–27.3 mm SL, paratypes of Corydoras urucu Britto, Wosiacki & Montag, 2009. Hoplisoma weitzmani: USNM 206018, 1, 38.5 mm SL, paratype of Corydoras weitzmani Nijssen, 1971. Hoplisoma xinguense: USNM 205870, 1, 27.9 mm SL, paratype of Corydoras xinguensis Nijssen, 1972. Osteogaster: Osteogaster aenea: USNM 1116, lectotype of Hoplosoma aeneum Gill, 1858, 38.2 mm SL; USNM 92819, 1, 49.5 mm SL, paralectotype; USNM 205649, 3, 32.7–44.9 mm SL, paralectotypes. Osteogaster eques: MCZ 8204, 4 of 12, 37.6–44.4 mm SL, paratypes of Corydoras eques Steindachner, 1876. Osteogaster hephaestus: MZUSP 119087, holotype of Corydoras hephaestus Ohara, Tencatt & Britto, 2016, 22.6 mm SL. Osteogaster maclurei: MUSM 70671, holotype of Corydoras maclurei, Tencatt, Gomes & Evers, 2023, 37.0 mm SL. Osteogaster melanotaenia: BMNH 1909.7.23.41, lectotype of Corydoras melanotaenia Regan, 1912, 38.3 mm SL; BMNH 1909.7.23.42, 1, 30.1 mm SL, paralectotype. Osteogaster rabauti: MNRJ 3626, holotype of Corydoras myersi Miranda Ribeiro, 1942, 46.0 mm SL; USNM 163252, 2, both 37.0 mm SL, paratypes of Corydoras myersi Miranda Ribeiro, 1942. Osteogaster zygata Eigenmann & Allen, 1942: MZUSP 30858, 4 of 15, 41.7–47.3 mm SL. Osteogaster sp. CW68: MNRJ 55728, 56 of 57, 23.1–38.5 mm SL, 1 c&s of 57, 40.9 mm SL. Scleromystax: Scleromystax barbatus: UFRJ 4441, 1 c&s, unmeasured, disarticulated specimen; UFRJ 4457, 2, unmeasured, disarticulated specimens. Scleromystax lacerdai: MNRJ 26017, 4 c&s of 17, 17.9–36.3 mm SL. Scleromystax macropterus: UFRJ 442, 2 c&s, 34.4 mm SL (the other unmeasured, disarticulated specimen). Scleromystax prionotos: UFRJ 4431, 1 c&s, unmeasured, disarticulated specimen. Scleromystax reisi: MNRJ 43857, 2 of 4, 41.9–47.2 mm, 2 c&s of 4, 38.3–38.7 mm SL, paratypes of Scleromystaxreisi Britto, Fukakusa & Malabarba, 2016. Scleromystax salmacis: MCP 28729, 3 c&s of 24, 23.9–45.6 mm SL.
ACKNOWLEDGEMENTS
This work is dedicated to Eric Bodrock, dear friend and renowned Corydoradinae breeder, for making the expedition to Jacareacanga, Pará, possible, as well as to Marcos Pinheiro, local fishermen in Jacareacanga for his invaluable help with fieldwork. The Universidade Federal de Mato Grosso (UFMT) provided logistical support. The authors are grateful to Carla Pavanelli (NUP), Carlos Lucena and Margarete Lucena (MCP), Cláudio Oliveira (LBP), Mário de Pinna, Aléssio Datovo, Michel Gianeti, Murilo Pastana and Osvaldo Oyakawa (MZUSP), Kris Murphy, Sandra Raredon and Jeffrey Clayton (USNM), Mark Sabaj and Mariangeles Arce (ANSP), James Maclaine and Oliver Crimmen (BMNH), and Otávio Froehlich (in memoriam) (ZUFMS) for hosting museum visits and loaning of material. To Emanuel Neuhaus (MNRJ), Francisco Severo-Neto and Thomaz Sinani (ZUFMS-PIS), Carlos Lucena and Héctor Vera-Alcaraz (MCP), Cláudio Oliveira, Ricardo Britzke, Fábio Roxo, Bruno Melo and Gabriel Silva (LBP), and Willian Ohara, Vinícius Espíndola and Túlio Teixeira (MZUSP) for generously welcoming LFCT during museum visits. To Fernando Vaz-de-Mello and Jorge Arias from the Laboratório de Scarabaeoidologia (UFMT) for allowing the use and general support of the photomontage equipment Leica M205C (subproject EECBio UFMT/Finep #01.12.0359.00), respectively. This study was partially supported by INCT - Peixes, funded by MCTIC/CNPq (proc. 405706/2022-7) through the sub-project “Peixes de Mato Grosso: preenchendo lacunas de coleta em riachos de cabeceira das bacias do alto Rio Paraguai e Rio Amazonas (incluindo sistema Tocantins-Araguaia)”. To the members of the fish keeping groups Corydoras World (United Kingdom), Catfish Study Group (United Kingdom), Internationale Gemeinschaft Barben Salmler Schmerlen Welse e.V. (Germany), Potomac Valley Aquarium Society (United States of America), Ohio Cichlid Association (USA), Greater Pittsburgh Aquarium Society, Inc. (USA), and All Oddball Aquatics (USA) for the invaluable support to LFCT. The Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES; proc. #88887.902472/2023–00) provided fellowship to VCG, and the Conselho Nacional de Desenvolvimento Científico e Tecnológico provided financial support to MRB (CNPq; proc. #311294/2021–9).
REFERENCES
-
Alexandrou MA, Oliveira C, Maillard M, McGill RAR, Newton J, Creer S, Taylor MI. Competition and phylogeny determine community structure in Müllerian co-mimics. Nature. 2011; 469(7328):84–89. https://doi.org/10.1038/nature09660
» https://doi.org/10.1038/nature09660 -
Armbruster JW, Page LM. Convergence of a cryptic saddle pattern in benthic freshwater fishes. Environ Biol Fish. 1996; 45:249–57. https://doi.org/10.1007/BF00003092
» https://doi.org/10.1007/BF00003092 -
Arratia G, Gayet M. Sensory canals and related bones of Tertiary siluriform crania from Bolivia and North America and comparison with recent forms. J Vertebr Paleontol. 1995; 15(3):482–505. https://doi.org/10.1080/02724634.1995.10011243
» https://doi.org/10.1080/02724634.1995.10011243 - Asai R, Taguchi E, Kume Y, Saito M, Kondo S. Zebrafish leopard gene as a component of the putative reaction–diffusion system. Mech Dev. 1999; 89:87–92.
-
Ballen GA, de Pinna MCC. A standardized terminology of spines in the order Siluriformes (Actinopterygii: Ostariophysi). Zool J Linn Soc. 2021; 194(2):601–25. https://doi.org/10.1093/zoolinnean/zlab008
» https://doi.org/10.1093/zoolinnean/zlab008 -
Beckmann C, Biro PA, Post J.R. Asymmetric impact of piscivorous birds on size-structured fish populations. Can J Zool. 2006; 84(11):1584–93. https://doi.org/10.1139/z06-151
» https://doi.org/10.1139/z06-151 -
Bentley RF, Grant S, Tencatt LFC. A new arc-striped species of Corydoras Lacépède, 1803 (Teleostei: Callichthyidae) from the Peruvian Amazon. Zootaxa. 2021; 4948(2):184–200. https://doi.org/10.11646/zootaxa.4948.2.2
» https://doi.org/10.11646/zootaxa.4948.2.2 -
Bono A, Tencatt LFC, Alonso F, Lehmann A P. Redescription of Corydoras undulatus Regan, 1912 (Siluriformes: Callichthyidae), with comments on the identity of Corydoras latus Pearson, 1924. PLoS ONE. 2019; 14(1):e0211352. https://doi.org/10.1371/journal.pone.0211352
» https://doi.org/10.1371/journal.pone.0211352 - Booth CL. Evolutionary significance of ontogenetic colour change in animals. Biol J Linn Soc. 1990; 40(2):125–63.
- Britto MR. Two new species of Aspidoras (Siluriformes: Callichthyidae) from Central Brazil. Ichthyol Explor Freshw. 1998; 8(4):359–68.
-
Britto MR. Phylogeny of the subfamily Corydoradinae Hoedeman, 1952 (Siluriformes: Callichthyidae), with a definition of its genera. Proc Acad Nat Sci Phila. 2003; 153(1):119–54. https://doi.org/10.1635/0097-3157(2003)153[0119:POTSCH]2.0.CO;2
» https://doi.org/10.1635/0097-3157(2003)153[0119:POTSCH]2.0.CO;2 -
Britto MR, Castro RMC. A new corydoradine catfish (Siluriformes: Callichthyidae) from the upper Paraná and São Francisco: the sister-group of Brochis and most of Corydoras species. Copeia. 2002; 2002(4):1006–15. https://doi.org/10.1643/0045-8511(2002)002[1006:NCCSCF]2.0.CO;2
» https://doi.org/10.1643/0045-8511(2002)002[1006:NCCSCF]2.0.CO;2 -
Britto MR, Lima FCT. Corydoras tukano, a new species of Corydoradine catfish from the rio Tiquié, upper rio Negro basin, Brazil (Ostariophysi: Siluriformes: Callichthyidae). Neotrop Ichthyol. 2003; 1(2):83–91. https://doi.org/10.1590/S1679-62252003000200002
» https://doi.org/10.1590/S1679-62252003000200002 -
Britto MR, Lima FC, Hidalgo MH. Corydoras ortegai, a new species of corydoradine catfish from the lower río Putumayo in Peru (Ostariophysi: Siluriformes: Callichthyidae). Neotrop Ichthyol. 2007; 5(3):293–300. https://doi.org/10.1590/S1679-62252007000300009
» https://doi.org/10.1590/S1679-62252007000300009 -
Britto MR, Lima FCT, Santos ACA. A new Aspidoras (Siluriformes: Callichthyidae) from rio Paraguaçu basin, Chapada Diamantina, Bahia, Brazil. Neotrop Ichthyol. 2005; 3(4):473–79. https://doi.org/10.1590/S1679-62252005000400004
» https://doi.org/10.1590/S1679-62252005000400004 -
Britto MR, Reis RE. A new Scleromystax species (Siluriformes: Callichthyidae) from coastal rivers of Southern Brazil. Neotrop Ichthyol. 2005; 3(4):481–88. https://doi.org/10.1590/S1679-62252005000400005
» https://doi.org/10.1590/S1679-62252005000400005 -
Britto MR, Wosiacki WB, Montag LFA. A new species of Corydoradinae catfish (Ostariophysi: Siluriformes: Callichthyidae) from Rio Solimões Basin, Brazil. Copeia. 2009; 2009(4):684–89. https://doi.org/10.1643/CI-08-228
» https://doi.org/10.1643/CI-08-228 - Cott HB. Adaptive Coloration in Animals. Methuen: Oxford University Press; 1940.
-
Dias AC. Molecular identification and phylogenetic relations of the family Callichthyidae (Actinopterygii: Siluriformes). [PhD Thesis]. Botucatu: Universidade Estadual Paulista “Júlio de Mesquita Filho”; 2022. Available from: http://hdl.handle.net/11449/217056
» http://hdl.handle.net/11449/217056 -
Dias AC, Tencatt LFC, Roxo FF, Silva GC, Santos SA, Britto MR, Taylor MI, Oliveira C. Phylogenomic analyses in the complex Neotropical subfamily Corydoradinae (Siluriformes: Callichthyidae) with a new classification based on morphological and molecular data. Zool J Linn Soc. 2024; zlae053. https://doi.org/10.1093/zoolinnean/zlae053
» https://doi.org/10.1093/zoolinnean/zlae053 - Eigenmann CH, Eigenmann RS. A revision of the South American Nematognathi or cat-fishes. Occas pap Calif Acad Sci. 1890; 1:1–508.
- Ellis MD. The plated nematognaths. Anna Carnegie Mus. 1913; 8:384–413.
- Endler JA. A predator’s view of animal color patterns. Evol Biol. 1978; 11(3):319–64.
- Endler JA. Frequency-dependent predation, crypsis and aposematic coloration. Phil Trans R Soc Lond. 1988; 319:505–23.
-
Endler J, Mappes J. Predator mixes and the conspicuousness of aposematic signals. Am Nat. 2004; 163(4):532–47. https://doi.org/10.1086/382662
» https://doi.org/10.1086/382662 -
Espíndola VC, Tencatt LFC, Pupo FM, Villa-Verde L, Britto MR. From the inside out: a new species of armoured catfish Corydoras with the description of poorly-explored character sources (Teleostei, Siluriformes, Callichthyidae). J Fish Biol. 2018; 92(5):1463–86. https://doi.org/10.1111/jfb.13602
» https://doi.org/10.1111/jfb.13602 - Fine ML, Ladich F. Sound production, spine locking and related adaptations. In: Arratia G, Kapoor BG, Chardon M, Diogo R, editors. Catfishes. Enfield: Science Publishers; 2003. p.249–90.
- Fricke HW. Juvenile-adult colour patterns and coexistence in the territorial coral reef fish Pomacanthus imperator Mar Ecol. 1980; 1(2):133–41.
-
Fricke R, Eschmeyer WN, Fong JD. Eschmeyer’s catalog of fishes: species by family/subfamily [Internet]. San Francisco: California; 2024. Available from: https://researcharchive.calacademy.org/research/ichthyology/catalog/SpeciesByFamily.asp
» https://researcharchive.calacademy.org/research/ichthyology/catalog/SpeciesByFamily.asp - Fuller IAM. Breeding Corydoradinae catfish. Kidderminster: Ian Fuller Enterprises; 2012.
- Gosline WA. A revision of the Neotropical catfishes of the family Callichthyidae. Stanford Ichthyol Bull. 1940; 2:1–36.
- Grant S. Corydoras CW004. JCSG. 2019; 20(1):8–10.
- Grant S. Hovering behaviour in Corydoras CW006. JCSG. 2020; 21(1):27–29.
- Grant S. Envenomation and aposematism in Corydoradinae JCSG. 2022; 23(1):29–31.
-
Hamel MJ, Spurgeon JJ, Steffensen KD. Uncovering unique plasticity in life history of an endangered centenarian fish. Sci Rep. 2020; 10:12866. https://doi.org/10.1038/s41598-020-69911-1
» https://doi.org/10.1038/s41598-020-69911-1 - Huysentruyt F, Adriaens D. Descriptive osteology of Corydoras aeneus (Siluriformes: Callichthyidae). Cybium. 2005; 29:261–73.
-
International Union for Conservation of Nature (IUCN) Guidelines for using the IUCN Red List categories and criteria. Version 15.1 [Internet]. Gland; 2022. Available from: http://cmsdocs.s3.amazonaws.com/RedListGuidelines.pdf
» http://cmsdocs.s3.amazonaws.com/RedListGuidelines.pdf -
Jacquemin SJ, Pyron M. A century of morphological variation in Cyprinidae fishes. BMC Ecol. 2016; 16:48. https://doi.org/10.1186/s12898-016-0104-x
» https://doi.org/10.1186/s12898-016-0104-x - Kiehl E, Rieger C, Greven H. Axillary gland secretions contribute to the stress-induced discharge of a bactericidal substance in Corydoras sterbai (Callichthyidae, Siluriformes). Verh Ges Oekol Ich. 2006; 5:111–15.
- Knaack J. Beitraege zur Kenntnis der Callichthyidae (Teleostei: Siluriformes). III. Corydoras longipinnis sp. n. – ein neuer Panzerwels aus dem río Dulce in Argentinien (Teleostei: Siluriformes: Callichthyidae). Vertebr Zool. 2007; 57:35–55.
- Kondo S, Asai R. A reaction–diffusion wave on the skin of the marine angelfish Pomacanthus Nature. 1995; 376:765–68.
-
Leclercq E, Taylor JF, Migaud H. Morphological skin colour changes in teleosts. Fish Fish. 2010; 11(2):159–93. https://doi.org/10.1111/j.1467-2979.2009.00346.x
» https://doi.org/10.1111/j.1467-2979.2009.00346.x -
Lofeu L, Anelli V, Straker LC, Kohlsdorf T. Developmental plasticity reveals hidden fish phenotypes and enables morphospace diversification. Evolution. 2021; 75(5):1170–88. https://doi.org/10.1111/evo.14221
» https://doi.org/10.1111/evo.14221 - Lundberg JG. The evolutionary history of North American catfishes, family Ictaluridae. [PhD Thesis]. Michigan: The University of Michigan; 1970.
-
Maan ME, Sefc KM. Colour variation in cichlid fish: developmental mechanisms, selective pressures and evolutionary consequences. Semin Cell Dev Biol. 2013; 24(6–7):516–28. https://doi.org/10.1016/j.semcdb.2013.05.003
» https://doi.org/10.1016/j.semcdb.2013.05.003 -
Mahon JL. The advantage of juvenile coloration in reef fishes. [PhD Thesis]. Honolulu: University of Hawaii at Manoa; 1998. Available from: https://scholarspace.manoa.hawaii.edu/items/a666738f-59bf-4459-9c6f-b38ae9a2c8df/full
» https://scholarspace.manoa.hawaii.edu/items/a666738f-59bf-4459-9c6f-b38ae9a2c8df/full -
Marburger S, Alexandrou MA, Taggart JB, Creer S, Carvalho G, Oliveira C, Taylor MI. Whole genome duplication and transposable element proliferation drive genome expansion in Corydoradinae catfishes. Proc R Soc B Biol Sci. 2018; 285(1872):20172732. https://doi.org/10.1098/rspb.2017.2732
» https://doi.org/10.1098/rspb.2017.2732 - Nakatani K, Agostinho AA, Baumgartner G, Bialetzki A, Sanches PV, Makrakis MC, Pavanelli CS. Ovos e larvas de peixes de água doce: desenvolvimento e manual de identificação. Maringá: Eletrobrás/UEM; 2001.
- Neal TJ. A Test of the function of juvenile color patterns in the pomacentrid fish Hypsypops rubicundus (Teleostei: Pomacentridae). Pac Sci. 1993; 47(3):240–47.
- Nijssen H. Revision of the Surinam catfishes of the genus Corydoras Lacépède, 1803 (Pisces, Siluriformes, Callichthyidae). Beaufortia. 1970; 18:1–75.
- Nijssen H, Isbrücker IJH. Notes on the Guiana species of Corydoras Lacépède, 1803, with descriptions of seven new species and designation of a neotype for Corydoras punctatus (Bloch, 1794) (Pisces, Cypriniformes, Callichthyidae). Zool Meded. 1967; 42(5):21–50.
- Nijssen H, Isbrücker IJH. A review of the genus Corydoras Lacépède, 1803 (Pisces, Siluriformes, Callichthyidae). Bijdr Dierkd. 1980a; 50(1):190–220.
- Nijssen H, Isbrücker IJH Aspidoras virgulatus n. sp., a plated catfish from Espírito Santo, Brazil (Pisces, Siluriformes, Callichthyidae). Bull Zool Mus Univ Amst. 1980b; 7(13):133-39.
- Nijssen H, Isbrücker IJH. Sept espèces nouvelles de poissons-chats cuirassés du genre Corydoras Lacepède, 1803, de Guyane française, de Bolivie, d’Argentine, du Surinam et du Brésil (Pisces, Siluriformes, Callichthyidae). RFAH. 1983; 10(3):73–82.
- Nijssen H, Isbrücker IJH. Review of the genus Corydoras from Peru and Ecuador (Pisces, Siluriformes, Callichthyidae). Stud Neotrop Fauna Environ. 1986; 21(1–2):1–68.
- Nilsson L. Food-seeking activity of south Swedish diving ducks in the non-breeding season. Oikos. 1970; 21:145–54.
- Nilsson PA, Brönmark C, Pettersson LB. Benefits of a predator-induced morphology in crucian carp. Oecologia. 1995; 104:291–96.
- Nüsslein-Volhard C, Singh AP. How fish color their skin: a paradigm for development and evolution of adult patterns. Bioessays. 2017; 39(3):160023.
-
Olendorf R, Rodd F, Punzalan D, Houde AE, Hurt C, Reznick DN, Hughes KA. Frequency-dependent survival in natural guppy populations. Nature. 2006; 441:633–36. https://doi.org/10.1038/nature04646
» https://doi.org/10.1038/nature04646 - Pearson NE. The fishes of the eastern slope of the Andes. I. The fishes of the Rio Beni basin, Bolivia, collected by the Mulford expedition. IUJUR. 1924; 11(64):1–83.
-
Pohlmann K, Grasso FW, Breithaupt T. Tracking wakes: the nocturnal predatory strategy of piscivorous catfish. Proc Natl Acad Sci USA. 2001; 98(13):7371–74. https://doi.org/10.1073/pnas.121026298
» https://doi.org/10.1073/pnas.121026298 -
Prada C, Schizas NV, Yoshioka PM. Phenotypic plasticity or speciation? A case from a clonal marine organism. BMC Evol Biol. 2008; 8:47. https://doi.org/10.1186/1471-2148-8-47
» https://doi.org/10.1186/1471-2148-8-47 - Randall JE. Shore fishes of Hawai’i. Honolulu: Natural World Press; 1996.
- Reis RE. Revision of the Neotropical catfish genus Hoplosternum (Ostariophysi: Siluriformes: Callichthyidae), with the description of two new genera and three new species. Ichthyol Explor Freshw. 1997; 7(4):299–326.
-
Reis RE. Anatomy and phylogenetic analysis of the neotropical callichthyid catfishes (Ostariophysi, Siluriformes). Zool J Linn Soc. 1998; 124(2):105–68. https://doi.org/10.1111/j.1096-3642.1998.tb00571.x
» https://doi.org/10.1111/j.1096-3642.1998.tb00571.x - Reis RE. Family Callichthyidae (Armored catfishes). In: Reis RE, Kullander SO, Ferraris Jr. CJ, editors. Check list of the freshwater fishes of South and Central America. Porto Alegre: Edipucrs; 2003. p.291–309.
-
Sabaj MH. Codes for Natural History Collections in Ichthyology and Herpetology. (online supplement). Version 9.5. American Society of Ichthyologists and Herpetologists, Washington, DC. 2023. Available from: https://asih.org
» https://asih.org -
Sazima I, Carvalho LN, Mendonça FP, Zuanon J. Fallen leaves on the water-bed: diurnal camouflage of three night active fish species in an Amazonian streamlet. Neotrop Ichthyol. 2006; 4(1):119–22. https://doi.org/10.1590/S1679-62252006000100013
» https://doi.org/10.1590/S1679-62252006000100013 -
Schaefer AS. Homology and evolution of the opercular series in the loricarioid catfishes (Pisces: Siluroidei). J Zool. 1988; 214(1):81–93. https://doi.org/10.1111/j.1469-7998.1988.tb04988.x
» https://doi.org/10.1111/j.1469-7998.1988.tb04988.x -
Schaefer SA, Aquino AE. Postotic laterosensory canal and pterotic branch homology in catfishes. J Morphol. 2000; 246(3):212–27. https://doi.org/10.1002/1097-4687(200012)246:3%3C212::aid-jmor5%3E3.0.co;2-s
» https://doi.org/10.1002/1097-4687(200012)246:3%3C212::aid-jmor5%3E3.0.co;2-s -
Slobodian V, Pastana MN. Description of a new Pimelodella (Siluriformes: Heptapteridae) species with a discussion on the upper pectoral girdle homology of Siluriformes. J Fish Biol. 2018; 93(5):901–16. https://doi.org/10.1111/jfb.13795
» https://doi.org/10.1111/jfb.13795 -
Spadella MA, Desan SP, Henriques TCBPO, Oliveira C. Variation in male reproductive system characters in Corydoradinae (Loricarioidei: Callichthyidae) reflects the occurrence of different lineages in this subfamily. Neotrop Ichthyol. 2017; 15(1):e160039. https://doi.org/10.1590/1982-0224-20160039
» https://doi.org/10.1590/1982-0224-20160039 -
Springer VG, Johnson GD. Use and advantages of ethanol solution of alizarin red S dye for staining bone in fishes. Copeia. 2000; 2000(1):300–01. https://doi.org/10.1643/0045-8511(2000)2000[0300:UAAOES]2.0.CO;2
» https://doi.org/10.1643/0045-8511(2000)2000[0300:UAAOES]2.0.CO;2 - Taylor WR, Van Dyke GC. Revised procedures for staining and clearing small fishes and other vertebrates for bone and cartilage study. Cybium. 1985; 9(2):107–19.
-
Tencatt LFC, Britto MR. A new Corydoras Lacépède, 1803 (Siluriformes: Callichthyidae) from the rio Araguaia basin, Brazil, with comments about Corydoras araguaiaensis Sands, 1990. Neotrop Ichthyol. 2016; 14(1):e150062. https://doi.org/10.1590/1982-0224-20150062
» https://doi.org/10.1590/1982-0224-20150062 -
Tencatt LFC, Britto MR, Isbrücker IJH, Pavanelli CS. Taxonomy of the armored catfish genus Aspidoras (Siluriformes: Callichthyidae) revisited, with the description of a new species. Neotrop Ichthyol. 2022b; 20(3):e220040. https://doi.org/10.1590/1982-0224-2022-0040
» https://doi.org/10.1590/1982-0224-2022-0040 -
Tencatt LF, Britto MR, Pavanelli CS. A new long-finned Corydoras Lacépède, 1803 (Siluriformes: Callichthyidae) from the lower rio Paraná basin, Brazil. Neotrop Ichthyol. 2014a; 12(1):71–79. https://doi.org/10.1590/S1679-62252014000100007
» https://doi.org/10.1590/S1679-62252014000100007 -
Tencatt LF, Britto MR, Pavanelli, CS. A new species of Corydoras Lacépède, 1803 (Siluriformes: Callichthyidae) from the upper rio Paraná basin, Brazil. Neotrop Ichthyol. 2014b; 12(1):89–96. https://doi.org/10.1590/S1679-62252014000100009
» https://doi.org/10.1590/S1679-62252014000100009 -
Tencatt LFC, Couto OLP, Santos SA, Sousa LM. A new long-snouted Corydoras (Siluriformes: Callichthyidae) from the rio Xingu and rio Tapajós basins, Brazilian Amazon. Neotrop Ichthyol. 2024a; 22(1):e230112. https://doi.org/10.1590/1982-0224-2023-0112
» https://doi.org/10.1590/1982-0224-2023-0112 -
Tencatt LFC, Evers HG. A new species of Corydoras Lacépède, 1803 (Siluriformes: Callichthyidae) from the río Madre de Dios basin, Peru. Neotrop Ichthyol. 2016; 14(1):13–26. https://doi.org/10.1590/1982-0224-20150019
» https://doi.org/10.1590/1982-0224-20150019 -
Tencatt LFC, Gomes VDC, Evers HG. A new species of Corydoras (Siluriformes: Callichthyidae) from the rio Madre de Dios basin, Peruvian Amazon, with comments on Corydoras aeneus identity. Neotrop Ichthyol. 2023; 21(2):e230023. https://doi.org/10.1590/1982-0224-2023-0023
» https://doi.org/10.1590/1982-0224-2023-0023 -
Tencatt LFC, Grant S, Bentley RF. A new color-changing species of Corydoras (Siluriformes: Callichthyidae) from the rio Jutaí, Brazilian Amazon. Neotrop Ichthyol. 2023b; 21(4):e230105. https://doi.org/10.1590/1982-0224-2023-0105
» https://doi.org/10.1590/1982-0224-2023-0105 -
Tencatt LFC, Lima FCT, Britto MR. Deconstructing an octogenarian misconception reveals the true Corydoras arcuatus Elwin 1938 (Siluriformes: Callichthyidae) and a new Corydoras species from the Amazon basin. J Fish Biol. 2019; 95(2):453–71. https://doi.org/10.1111/jfb.13980
» https://doi.org/10.1111/jfb.13980 -
Tencatt LFC, Ohara WM. A new long-snouted species of Corydoras Lacépède, 1803 (Siluriformes: Callichthyidae) from the rio Madeira basin. Zootaxa. 2016a; 4144(3):430–42. http://dx.doi.org/10.11646/zootaxa.4144.3.9
» http://dx.doi.org/10.11646/zootaxa.4144.3.9 -
Tencatt LFC, Ohara WM. Two new species of Corydoras Lacépède, 1803 (Siluriformes: Callichthyidae) from the rio Madeira basin, Brazil. Neotrop Ichthyol. 2016b; 14(1):139–54. https://doi.org/10.1590/1982-0224-20150063
» https://doi.org/10.1590/1982-0224-20150063 -
Tencatt LFC, Ohara WM, Sousa LMD, Britto MRD. Science and hobby joining forces for the discovery of three new Corydoras (Siluriformes: Callichthyidae) from the rio Tapajós basin, Brazil, with comments on Corydoras sp. CW111. Neotrop Ichthyol. 2022a; 20(3):e220070. https://doi.org/10.1590/1982-0224-2022-0070
» https://doi.org/10.1590/1982-0224-2022-0070 -
Tencatt LFC, Pavanelli CS. Redescription of Corydoras guapore Knaack, 1961 (Siluriformes: Callichthyidae), a midwater Corydoradinae species from the rio Guaporé basin. Neotrop Ichthyol. 2015; 13(2):287–96. https://doi.org/10.1590/1982-0224-20150018
» https://doi.org/10.1590/1982-0224-20150018 -
Tencatt LFC, Ruiz-Tafur M, Chuctaya J. A new masked Corydoras (Siluriformes: Callichthyidae) from the Itaya and Nanay river basins, Peruvian Amazon. Neotrop Ichthyol. 2024; 22(2):e240016. https://doi.org/10.1590/1982-0224-2024-0016
» https://doi.org/10.1590/1982-0224-2024-0016 -
Tencatt LFC, Santos SAD, Britto MR. Taxonomic review of the typical long-snouted species of Corydoras (Siluriformes: Callichthyidae) from the río de La Plata basin. Neotrop Ichthyol. 2020; 18(4):e200088. https://doi.org/10.1590/1982-0224-2020-0088
» https://doi.org/10.1590/1982-0224-2020-0088 -
Tencatt LFC, Santos SA, Evers H-G, Britto MR Corydoras fulleri (Siluriformes: Callichthyidae), a new catfish species from the rio Madeira basin, Peru. J Fish Biol. 2021; 99(2):614–28. https://doi.org/10.1111/jfb.14750
» https://doi.org/10.1111/jfb.14750 -
Tencatt LFC, Vera-Alcaraz HS, Britto MR, Pavanelli CS. A new Corydoras Lacépède, 1803 (Siluriformes: Callichthyidae) from the rio São Francisco basin, Brazil. Neotrop Ichthyol. 2013; 11(2):257–64. https://doi.org/10.1590/S1679-62252013000200003
» https://doi.org/10.1590/S1679-62252013000200003 -
Turing AM. The chemical basis of morphogenesis. Philos Trans R Soc Lond B Biol Sci. 1952; 327:37–72. https://doi.org/10.1098/rstb.1952.0012
» https://doi.org/10.1098/rstb.1952.0012 -
Vera-Alcaraz HS. Relações filogenéticas das espécies da família Callichthyidae (Ostariophysi, Siluriformes). [PhD Thesis]. Porto Alegre: Pontifícia Universidade Católica do Rio Grande do Sul; 2013. Available from: https://tede2.pucrs.br/tede2/handle/tede/263
» https://tede2.pucrs.br/tede2/handle/tede/263 -
Watanabe M, Iwashita M, Ishii M, Kurachi Y, Kawakami A, Kondo S, Okada N. Spot pattern of leopard Danio is caused by mutation in the zebrafish connexin41.8 gene. EMBO Rep. 2006; 7(9):893–97. https://doi.org/10.1038/sj.embor.7400757
» https://doi.org/10.1038/sj.embor.7400757
ADDITIONAL NOTES
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Zoobank Register
https://zoobank.org/DEF00A5C-D51C-44E2-8A0D-B91B70865CE6
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Ethical Statement
The type-specimens of both new species were collected under the license #85671–1 and #65628–5, granted to LFCT and WMO by the Sistema de Autorização e Informação em Biodiversidade (SISBIO), respectively.
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HOW TO CITE THIS ARTICLE
Tencatt LFC, Ohara WM, Carvalho V, Grant S, Britto M. Two exquisite new species of Hoplisoma (Siluriformes: Callichthyidae) from the rio Tapajós basin, Brazil, with a discussion on the morphology of the mesethmoid within Corydoradinae. Neotrop Ichthyol. 2025; 23(1):e240100. https://doi.org/10.1590/1982-0224-2024-0100
Publication Dates
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Publication in this collection
07 Apr 2025 -
Date of issue
2025
History
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Received
03 Oct 2024 -
Accepted
16 Dec 2024
