New tribe-level classification of Hypostominae (Loricariidae) based on optimization of morphological states on DNA-based relationships, with descriptions of three new tribes and two new genera

Abstract

Hypostominae tribe-level taxonomy is revised with new recognition and cladistic diagnoses of previously proposed family-level names for the Acanthicus (Acanthicini), Chaetostoma (Chaetostomatini), and Hemiancistrus (Spectracanthicini) clades. Three new tribes are described for the Peckoltia, Pseudancistrus,and ‘Pseudancistrus’ clades, with a new tribe erected for two new monotypic genera containing the sister species ‘Pseudancistrus’ sidereus and ‘P.’ pectegenitor. This third new tribe is known only from the upper Orinoco and Negro Rivers and is identifiable by having an accentuated keel on the caudal peduncle formed by dorsal laminae of the ventral plate series being strongly concave. The new genera are distinguishable by ‘P.’ pectegenitor having extremely long cheek odontodes reaching to the third plate of midventral plate series (vs. anterior to opercular opening in ‘P.’ sidereus) and 10 (vs. 7) branched dorsal-fin rays. We re-optimized morphological character-state change by mapping states previously used to infer evolutionary history onto a composite phylogenetic tree inferred from DNA-sequence data. This revealed the strong influence on morphology-based phylogenies of a correlated suite of opercular character states related to the mechanism for cheek odontode eversion. These states appear to be plesiomorphic within Hypostominae and to have been independently lost or reduced multiple times.

Keywords:
Character analysis; Morphology; Phylogeny; Pseudancistrus ; Venezuela

Resumo

A taxonomia no nível da tribo Hypostominae é revisada, com novo reconhecimento e diagnoses cladísticas de nomes previamente propostos em nível de família para os clados de Acanthicus (Acanthicini), Chaetostoma (Chaetostomatini) e Hemiancistus (Spectracanthicini). Três novas tribos são descritas para os clados de Peckoltia, Pseudancistrus e ‘Pseudancistrus’, com uma nova tribo erigida para dois novos gêneros monotípicos contendo as espécies irmãs ‘Pseudancistrus’ sidereus e ‘P.’ pectegenitor. Essa terceira nova tribo é conhecida somente das partes superiores dos rios Negro e Orinoco e pode ser identificada pela presença de uma quilha acentuada no pedúnculo caudal, formada por uma lâmina dorsal das placas da série ventral, que são fortemente côncavas. Os novos gêneros se distinguem por ‘P’. pectegenitor possuir odontódeos extremamente longos na região opercular, alcançando até a terceira placa da série médio-ventral (vs. anterior à abertura opercular em ‘P’. sidereus) e 10 (vs. 7) raios ramificados na nadadeira dorsal. Nós otimizamos novamente as mudanças de estado dos caracteres morfológicos colocando os estados previamente utilizados para inferir histórias evolutivas em uma árvore filogenética composta, inferida a partir de sequências de DNA. Isso revelou que um conjunto correlacionado de estados de caracteres operculares envolvidos com o mecanismo de eversão dos odontódeos da região opercular tem influência historicamente forte nas filogenias baseadas em morfologia. Esses estados parecem ser plesiomórficos dentro de Hypostominae, sendo perdidos, ou reduzidos, de maneira independente múltiplas vezes.

Palavras chave:
Análise de caracteres; Filogenia; Morfologia; Pseudancistrus ; Venezuela

INTRODUCTION

The suckermouth armored catfish family Loricariidae is the fifth-richest family of vertebrates and richest family of catfishes with over 1,060 species described (Fricke et al., 2024). Within Loricariidae, nearly half of all species (508; 48%) are assigned to the subfamily Hypostominae, with most remaining species being distributed across subfamilies Loricariinae (276; 26%), Hypoptopomatinae (263; 25%), Delturinae (7), Rhinelepinae (6), and Lithogeninae (3; Fricke et al., 2024).

Systematic study of Hypostominae was dominated by phenetic approaches (Regan, 1904; Isbrücker et al., 2001) until the first morphology-based cladistic analyses of Howes (1983) and Schaefer (1986), which marked the beginning of a gradual shift toward exclusively cladistic methodologies. Cladistic studies progressively encompassed more taxa and characters until the essentially comprehensive morphology-based analyses by Armbruster (2004a, 2008) and Armbruster, Taphorn (2011). DNA-based studies of Hypostominae began with a study of two mitochondrial rRNA gene regions (12S, 16S) and eight genera (Montoya-Burgos et al., 1997) and progressively included more loci and taxa, resulting most recently in the Lujan et al. (2015a) study of 49 genera using two mitochondrial and three nuclear markers and the Roxo et al. (2019) study of 30 genera using genome-wide ultraconserved elements. Regardless of taxonomic breadth and data magnitude, the revised systematic understanding of Hypostominae provided by DNA-based analyses has been largely consistent across studies, and consistently highly divergent from previous morphology-based inferences.

Comparisons of Hypostominae intergeneric relationships based on DNA versus morphology highlight two major types of discrepancy: morphological support for assigning species to genera that DNA-based studies later find to be paraphyletic, and morphological support for various distinct genera that later DNA-based studies find to be nested within an existing genus. Armbruster’s (2004a,b) lumping of many species into Pseudancistrus Bleeker, 1862 is an example of the former, with later DNA-based studies (Covain, Fisch-Muller, 2012; Lujan et al., 2015a) finding this broader Pseudancistrus to be polyphyletic. Examples of the latter include Lujan, Ambruster’s (2011) morphology-based description of Micracanthicus vandragti Lujan & Armbruster, 2011 and Soromonichthys stearleyi Lujan & Armbruster, 2011 as new genera, with Lujan et al. (2015a) finding the former to be nested within Hypancistrus Isbrücker & Nijssen, 1991 and the latter within Pseudolithoxus Isbrücker & Werner, 2001 (in Isbrücker et al., 2001). Deeper in the phylogeny, molecular analyses also support clades that would probably never have been considered based on morphology alone, such as the close relationship of Corymbophanes Eigenmann, 1909 with Hopliancistrus Isbrücker & Nijssen, 1989 (Lujan et al., 2015a). Corymbophanes lacks evertible cheek odontodes (Armbruster, Provenzano, 2000; Lujan et al., 2019) while Hopliancistrus has the most extreme cheek odontode eversion capability known (Oliveira et al., 2021).

Numerous such examples of molecular-morphological discrepancies just within Hypostominae illustrate the complexity of loricariid morphological evolution, with homoplastic characters appearing to have heavily influenced the classification schemes still in use today. These numerous and pervasive discrepancies illustrate the growing need for a thoroughly updated tribe and genus-level classification of Hypostominae based on an integration of results from both data sources. We begin that process by mapping character states described by Armbruster (2004a) onto the phylogeny of Lujan et al. (2015a), with additional species added per Lujan et al. (2015b, 2017, 2018, 2019). Results of this analysis provide a cladistic foundation for not only a revised classification, but also our description of three new tribes and two new genera. The resulting understanding of character state change across Hypostominae further demonstrates that several major loricariid clades currently lack morphological synapomorphies.

Two of the more enigmatic and recently described members of the now polyphyletic genus Pseudancistrus are Pseudancistrus sidereus Armbruster, 2004b and P. pectegenitor Lujan, Armbruster & Sabaj, 2007, both of which were described from the upper Orinoco and Negro River basins in southern Venezuela. Pseudancistrus pectegenitor is a wide-bodied, truncate species with a dark-brown base color, tiny light spots or vermiculations, a rounded dorsal fin with 10 or 11 branched dorsal-fin rays, and a caudal fin with a straight margin (Fig. 1A). Mature specimens have cheek odontodes that are among the longest seen in the Hypostominae (up to 60 mm) and a snout margined with enlarged odontodes up to 7 mm long. In contrast, Pseudancistrus sidereus is elongate for a hypostomine, has a dark gray base color with golden spots, a falcate dorsal fin with seven branched dorsal-fin rays, and a strongly asymmetrical caudal fin with the lower lobe much longer than the upper, and even mature males have very short cheek odontodes and no hypertrophied odontodes along the snout margin (Fig. 1B). Despite the dramatic morphological contrast between these species, molecular analyses have consistently strongly supported them as each other’s sister species, forming a clade that is distantly related to Pseudancistrussensu stricto (i.e., clade containing the type-species Pseudancistrus barbatus Valenciennes, 1840; Covain, Fisch-Muller, 2012; Lujan et al., 2015a; Roxo et al., 2019). To indicate this, Lujan et al. (2015a) referred to them as ‘Pseudancistrus’ with single quotation marks. Despite their radically divergent appearance, they do share a unique characteristic. Armbruster (2004b) first noted that the caudal peduncle of ‘P.’ sidereus has a strongly accentuated keel formed by the strongly concave dorsal laminae of the ventral series of plates (Fig. 2B). While a keel in this region of the caudal peduncle is not unusual in Hypostominae, due to the necessity that the ventral plates bend medially to follow the flattened ventral profile of the caudal peduncle, the degree of concavity and the accentuation of the curve was considered unique in ‘P.’ sidereus. This keel is even more strongly formed in ‘P.’ pectegenitor (Lujan et al., 2007, Fig. 2C).

FIGURE 1 |
A.Colossimystaxpectegenitor, Holotype, MCNG 54797, 241.6 mm SL. Photo by NKL. B.Stellantiasiderea, AUM 43443, 147.1 mm SL. The two genera are described below. Photo by M. H. Sabaj.

FIGURE 2 |
Caudal peduncles of A.Pseudancistrus nigrescens, AUM 35742, 137.2 mm SL; B.Stellantiasiderea, AUM 42185, 180.0 mm SL; and C.Colossimystax pectegenitor, paratype, AUM 42202, 227.0 mm SL. DL is the dorsal lamina of the indicated plate, and the keel lies just ventral. In A, there is only a slight keel (~3 plates) with the dorsal laminae straight to very slightly concave while the keel extends in front of the adipose fin in B and C and the dorsal laminae are concave.

While molecular phylogenies have revealed many new candidate genera in Hypostominae, these southern Venezuelan ‘Pseudancistrus’ species are among the best studied, most morphologically distinct, and easiest to diagnose from other Hypostominae genera. The species are clearly very different from one another such that one would likely not posit them to be closely related at first glance; thus, we erect two monotypic genera for these species.

MATERIAL AND METHODS

Specimens for osteological examination were either cleared and double-stained following Taylor, Van Dyke (1985) or µCT-scanned at varying resolutions (1.4–14.0 μm) using either a GE v|tome|x s240 dual tube 240/180 kV system (General Electric, Fairfield, CT, USA) or a Bruker Skyscan 1173 high-energy micro-CT (Bruker Inc, Billerica, MA, USA). CT data were edited, segmented, and colorized using VGStudio Max (v. 3.3–v2023.3; Volume Graphics, Heidelberg, Germany).

Counts and measurements follow Armbruster (2003). To determine character polarity a tree was constructed in Mesquite (Maddison, Maddison, 2023) based on Lujan et al. (2015a, 2015b, 2017, 2018, and 2019) with the characters of Armbruster (2004a, 2008) mapped to the phylogeny. Araichthys Zawadzki, Bifi & Mariotto, 2016was added per the characters listed in Zawadzki et al. (2016), Paulasquama Armbruster & Taphorn, 2011 per Armbruster, Taphorn (2011), and Hemiancistrus medians (Kner, 1854) per Armbruster et al. (2015) (matrix and tree in Tab. S1). Taxa were entered and a tree created in Mesquite v. 3.8 (Maddison, Maddison, 2023). The tree was transferred into MacClade v. 4.05 (Maddison, Maddison, 2002) to produce a table of character state changes (Tab. S2). Characters are predominantly osteological and meristic and are presented as the number: state or state change (i.e., 11: 0>1 represents character 11 changing from 0 to 1 at the node) with character numbers from Armbruster (2004a). Phylogenetic diagnoses are given as summaries of the character state changes on the tree. An additional comparative diagnosis summarizes the most useful external characters for visually distinguishing each taxon from other members of the Hypostominae. Clades for which tribe-level names are available have those names assigned and new tribes are described for the Peckoltia, Pseudancistrus,and ‘Pseudancistrus’ clades sensu Lujan et al. (2015a; relationships in fig. 3).

Geographic distributions were mapped in QGIS, v. 3.30.0 (QGIS Development Team, 2023). Rivers are from the HydroRIVERS v. 1.0 (Lehner, Grill, 2013), and river widths are represented as interpolated lines based on average discharge (DIS_AV_CMS) with only streams of six cubic meters per second or greater shown. Lakes are from the HydroLAKES v. 1 (Messager et al., 2016). Digital Elevation Model and Hillshade from Mapzen (https://www.mapzen.com). Country borders are from NaturalEarth (1:10m, file ne_10m_admin_countires, v. 5.1.1, naturalearthdata.com). Localities are from Armbruster (2004b), Lujan et al. (2007), and additional records added into the AUM database since publication. Museum acronyms are per Sabaj (2020).

RESULTS

Tribes. Four previously recognized family-level names are recognized for the following clades as named in Lujan et al. (2015a): Acanthicini Bleeker, 1862 for the Acanthicus Clade, Chaetostomatini Fowler, 1958 for the Chaetostoma clade, Lithoxini Isbrücker, 1980 for the Lithoxus clade (also recognized in Lujan et al., 2018), and Spectracanthicini Isbrücker & Nijssen, 1989 for the Hemiancistrus clade. We additionally describe three new tribes (Peckoltini, Pseudancistrini, and Stellantini) for the Peckoltia, Pseudancistrus,and ‘Pseudancistrus’ clades sensu Lujan et al. (2015a) as well as two new genera for Stellantini, new tribe.

Phylogeny. Tribe-level nodes for Acanthicini (8 characters), Lithoxini (31 characters), and Chaetostomatini (18 characters) were well supported following our placement of the morphological characters of Armbruster (2004a, 2008) on the composite molecular phylogeny. Many other nodes were supported by few or no character states (Fig. 3). For example, Peckoltini and its relationship with Hypostomini is not supported by any characters and Hypostomini is supported by only one. Within Ancistrini, no characters support the clade of Corymbophanes, Yaluwak, Araichthys, Cryptancistrus, Hopliancistrus,and Guyanancistrus nor that clade plus Dekeyseria. Also in Ancistrini, no characters support the clade of Neblinichthys plus Paulasquama nor that clade plus Lithoxancistrus. The clade of Neblinichthys, Paulasquama,and Lithoxancistrus is supported as sister to the remaining Ancistrini by three characters; however, in other analyses we have run, this clade is not part of the Ancistrini and will need further exploration. Taxa that were not supported within their current clades in the morphological analyses often have very strong support because what had been synapomorphies for larger clades are now autapomorphies for the individual elements. Examples include Guyanancistrus (18 characters), Corymbophanes (28), Paulasquama (17), Neblinichthys (11), Stellantia, new genus (9), Colossimystax,new genus (14), Panaque (19), Spectracanthicus (11), Parancistrus (15), and Scobinancistrus (9). The large numbers of characters along these branches suggests that morphological change in loricariids can be quite rapid.

Subfamily Hypostominae

Included tribes (with unrecognized tribes and subtribes listed as synonyms).

Acanthicini Bleeker, 1862–63:2. Synonym: Pseudacanthicini Isbrücker, 1980.

Ancistrini Kner, 1854:256. Synonyms: Corymbophanini Armbruster, 2004a, Hopliancistrini Isbrücker & Nijssen, 1989.

Chaetostomatini Fowler, 1958:14

Hypostomini Kner, 1853a:279. Synonyms: Plecostiformes Bleeker, 1862, Pterygoplichthyini Armbruster, 2004a

Lithoxini Isbrücker, 1980:77

Peckoltini, new tribe

Pseudancistrini, new tribe

Spectracanthicini Isbrücker & Nijssen, 1989

Stellantini, new tribe

FIGURE 3 |
Relationships of the clades of the genera of Hypostominae based on Lujan et al. (2015a,b, 2017, 2018, 2019). Stellantini, new tribe (abbreviated as Stell.), Peckoltini, new tribe, and Pseudancistrini, new tribe (abbreviated as Ps.) are described herein. Dashed lines represent species that were not available for morphological analysis. Numbers above branches represent the number of character state changes from Tab. S2.

Phylogenetic diagnosis. Accessory process offirst ceratobranchial same length as main body and wide (7:2, 8:2), interhyal contacting bony portion of quadrate (26:2), either hyomandibula, quadrate or both with projections towards one another or sutured (33:1), preopercle with short posterior section appearing to be oriented almost vertically (61:1), quadrate with posteroventral projection that extends below symplectic foramen (66:1), a sickle-shaped opercle (75:1; note that opercle shape is especially variable within Hypostominae), one or more plates between suprapreopercle and opercle (81:1), one small canal plate (83:1), canal plate contacting the suspensorium (85:1), two or more plates between canal plate and opercle (88:2), 8–11 vertebrae from first normal neural spine behind dorsal fin up to, but not including, the hypural plate (121:2), ventral half of hypural plate longer than dorsal (123:1), reversal to a V-shaped spinelet (148:0), anterolateral process of basipterygium wide through entire length (169:1), posterovenral ridge of basipterygium present (173:1), hypertrophied cheek odontodes present regardless of season or sex (183:2), fully or slightly evertible cheek plates (184:1–2; ability to at least partially evert cheek plates is unique to Hypostominae with the possible exception of ‘Pseudancistrus’ genisetiger), pectoral fin inserted ventrally such that it is aligned with and reaches or overlaps the pelvic fin (190:1; only seen in Pogonopoma outside of Hypostominae and reversed in Corymbophanes).

Comparative diagnosis. There are no universal character states that diagnose all Hypostominae from all other Loricariidae. The most widely diagnostic character states are cheek plates that evert forming a 30° to just greater than 90° from side of head (vs. not evertible; angle depends on species) and pectoral fin inserted ventrally such that it is aligned with and reaches or overlaps the pelvic fin (vs. pectoral fins distinctly dorsal to pelvic fins in all loricariids except Pogonopoma; Corymbophanes of the Hypostominae has the pectoral fins just slightly dorsal to the pelvics). Hypostominae can be separated from Lithogeninae by having the body fully plated (vs. anterior plates missing or non-overlapping); from Delturinae by having an adipose-fin spine followed by a membrane or a postdorsal ridge made of azygous plates with maximally a very small membrane (vs. postdorsal ridge made of azygous plates followed by an adipose-fin spine and membrane); from Rhinelepinae and Loricariinae by generally having an adipose fin or postdorsal ridge of azygous plates (vs. adipose fin and postdorsal ridge absent), from Rhinelepinae by generally having an iris operculum (vs. absent, some hypostomines lack an iris operculum, but they all have adipose fins or postdorsal ridges); from Loricariinae by generally not being extremely dorsoventrally flattened and elongated (only exceptions may be members of Lithoxini, which have evertible cheek plates present vs. absent and an adipose fin, and Isorineloricaria which has an adipose fin and five rows of plates on the caudal peduncle vs. three); from Hypoptopomatinae (except Neoplecostomini) by having maximally the lateral portion of the pectoral girdle exposed and supporting odontodes (vs. most or all of pectoral girdle exposed and supporting odontodes); from Hypoptopomatinae: Neoplecostomini by having hypertrophied odontodes generally absent along the snout of nuptial males or, when hypertrophied odontodes are present, they are not in thick integument (vs. generally having males with hypertrophied snout odontodes that are embedded in integument skin); and from ‘Pseudancistrus’ genesetiger and ‘P.’ papariae by having three or five rows of plates on the caudal peduncle (vs. four), and by either not having hypertrophied odontodes along the snout or on the cheek or having them clearly separated by plates contiguous with remaining plates of the snout and head (vs. hypertrophied snout and cheek odontodes supported by deeply embedded, flesh-covered, hidden plates that are sunken medially such that other snout plates and the opercle form a shelf dorsal and lateral to the bases of the odontodes).

Geographical distribution. Hypostominae is broadly distributed throughout cis-Andean South America from the Parana basin northward, and throughout trans-Andean drainages from the Tumbes basin in northern Peru to the Terraba River in eastern Costa Rica.

Tribe Acanthicini Bleeker, 1862-1863

Included genera.

Acanthicus Agassiz, 1829:2 (in Spix, Agassiz, 1829). Type-species: Acanthicus hystrix Spix & Agassiz, 1829.

Leporacanthicus Isbrücker, Nijssen, 1989:544. Type-species: Leporacanthicus galaxias Isbrücker & Nijssen, 1989.

Megalancistrus Isbrücker, 1980:52. Type-species: Chaetostoma gigas Boulenger, 1895.

Pseudacanthicus Bleeker, 1862:2. Type-species: Chaetostomus serratus Valenciennes, 1840 (in Cuvier, Valenciennes, 1840). Synonym: Stoniella Fowler, 1914.

Phylogenetic diagnosis. Anterohyal greatest width greater than half its length (1:1), loss of flap on quadrate extending below symplectic foramen (66:0), mesethmoid disk extending anterior to main body of mesethmoid (101:1), large fenestrae in compound pterotic (109:1, reversed in Leporacanthicus), tip of transverse process of Weberian complex centrum not contacting compound pterotic (135:1, reversed in Leporacanthicus), eight or more dorsal-fin rays (142:1), hypertrophied odontodes along snout margin (188>1), and keels of lateral plates well developed (198:1).

Comparative diagnosis. Acanthicini can be separated from all other Hypostominae except some Pterygoplichthys Gill, 1858 (particularly P. weberi) by having lateral-plate keels made of long, stout odontodes, from all other Hypostominae except Colossimystax and Pterygoplichthys by having more than seven dorsal-fin rays, and from Pterygoplichthys with keels by having strongly evertible cheek odontodes (vs. weakly evertible), by having fewer odontodes dorsal and ventral to keel rows (vs. odontodes normally distributed). In addition, Acanthicus can be separated from Pterygoplichthys by lacking an adipose fin (vs. adipose fin present), Acanthicus and Megalancistrus can be separated from Pterygoplichthys by having compound pterotic extending beyond posteriormost insertion of pectoral fin (vs. maximally through ~3/4 of pectoral-fin base); and Leporacanthicus and Pseudacanthicus can be separated from Pterygoplichthys by having 10 or fewer teeth per jaw ramus (vs. more than 20).

Geographical distribution. Restricted to larger, main river channel habitats in cis-Andean drainages from the Paraná and São Francisco basins northward, including the Amazon and Orinoco basins and north-flowing Guiana Shield basins.

Tribe Ancistrini Kner, 1854

Included genera.

Ancistrus Kner, 1854:272. Type-species: Hypostomus cirrhosus Valenciennes, 1836 (in Valenciennes, 1834–39). Synonyms: Pristiancistrus Fowler, 1945, Thysanocara, Regan, 1906, and Xenocara Regan, 1904.

Araichthys Zawadzki et al., 2016:362. Type-species: A. loro Zawadzki, Bifi & Mariotto, 2016.

Corymbophanes, Eigenmann, 1909:5. Type-species: Corymbophanes andersoni Eigenmann, 1909.

Cryptancistrus Fisch-Muller et al., 2018:50. Type-species: C. similis Fisch-Muller, Mol & Covain, 2018.

Dekeyseria , Rapp Py-Daniel, 1985:178. Type-species: D. amazonica Rapp Py-Daniel, 1985. Synonym: Zonancistrus Isbrücker, 2001 (in Isbrücker et al., 2001).

Guyanancistrus Isbrücker, 2001:19 (in Isbrücker et al., 2001). Type-species: Lasiancistrus brevispinis Heitmans, Nijssen & Isbrücker, 1983.

Hopliancistrus Isbrücker, Nijssen, 1989:543. Type-species: H. tricornis Isbrücker & Nijssen, 1989.

Lasiancistrus Regan, 1904:224. Type-species: Chaetostomus heteracanthus Günther, 1869. See Armbruster, 2005.

Neblinichthys, Ferraris et al., 1986:70. Type-species: N. pilosus Ferraris, Isbrücker & Nijssen, 1986.

Lithoxancistrus Isbrücker et al., 1988:14. Type-species: L. orinoco Isbrücker, Nijssen & Cala, 1988.

Paulasquama Armbruster, Taphorn, 2011:46. Type-species: P. callis Armbruster & Taphorn, 2011.

Pseudolithoxus Isbrücker, Werner, 2001:21 (in Isbrücker et al., 2001). Type-species: Lasiancistrus tigris Armbruster & Provenzano, 2000. Synonym: Soromonichthys Lujan & Armbruster, 2011.

Yaluwak Lujan, Armbruster, 2019 (in Lujan et al., 2019). Type-species: Yaluwak primus Lujan, Armbruster & Werneke (in Lujan et al., 2019).

Phylogenetic diagnosis. No characters unite tribe Ancistrini as all character state changes at the node are reversed in a majority of taxa. Character state changes found at the node are hypertrophied odontodes along snout margin (188:1), snout and pectoral-fin odontode sheaths separated from odontode forming short tentacules (208:1, 209:1).

Comparative diagnosis. The diversity of forms within Ancistrini results in no characteristics that can readily separate it from all other tribes. Ancistrus, Araichthys, Corymbophanes, Dekeyseria, Lasiancistrus, Neblinichthys,and Pseudolithoxus can be separated from all Hypostomini by having three rows of plates on the caudal peduncle (vs. five, rarely four).Araichthys, Corymbophanes,some Neblinichthys, and Yaluwak can be separated from most other Hypostominae by lacking an iris operculum (the dorsal flap that bifurcates the dorsal part of the eye in most loricariids). Hopliancistrus can be separated from all other Hypostominae by generally having three large, stout, continuously curved evertible cheek odontodes (vs. no hypertrophied cheek odontodes or more or less than three with odontodes generally slender and hooked only distally, not curved throughout). Cryptancistrus, Hopliancistrus,and Lasiancistrus can be separated from all other Hypostominae by having hypertrophied odontodes at anterior corner of snout (see Armbruster, 2005). Guyanancistrus is not readily diagnosable from other Hypostominae, see Fisch-Muller et al. (2018) for review.

Geographical distribution. Found in all cis-Andeandrainagesfrom the La Plata River basin northward (including Trinidad) and trans-Andean basins from southern Ecuador to just east of the Herrera Peninsula, Panamá.

Tribe Chaetostomatini Fowler, 1958

Included genera.

Andeancistrus Lujan et al., 2015b:652. Type-species: Chaetostomus platycephalus Boulenger, 1898.

Chaetostoma, Tschudi, 1846:25. Type-species: Chaetostomus loborhynchos Tschudi, 1846. Synonyms: Hypocolpterus Fowler, 1943, Lipopterichthys Norman, 1935, and Loraxichthys Salcedo, 2013.

Cordylancistrus Isbrücker, 1980:48. Type-species: Pseudancistrus torbesensis Schultz, 1944.

Dolichancistrus Isbrücker, 1980:47. Type-species: Pseudancistrus pediculatus Eigenmann, 1918 [a junior synonym of Dolichancistrus fuesslii (Steindachner, 1911].

Leptoancistrus, Meek, Hildebrand, 1916:254. Type-species: Acanthicus canensis Meek & Hildebrand, 1913.

Transancistrus Lujan et al., 2015b:657. Type-species: Cordylancistrus santarosensis Tan & Armbruster, 2012.

Phylogenetic diagnosis. Anterior edge of the anterohyal sinusoidal (2:1, reversed in Cordylancistrus torbesensis and Dolichancistrus cobrensis), mesial facing process on branchiostegal 3 (6:1, unique), reversal to a large interhyal (27:0), long opercular condyle of the hyomandibula (38:1), tall levator arcus palatini crest (44:2), mesial wall of metapterygoid channel much taller than lateral wall (55:1, reversed in Cordylancistrus torbesensis), ventral process on quadrate for articulation with canal plate (65:1), wide, blunt articular condyle of quadrate (67:1), bar-shaped opercle (75:2), maximum forward position of opercle to posterolateral corner of the quadrate (77:1, reversed in Andeancistrus and some Chaetostoma), canal plate covered in skin or plates and not directly supporting odontodes (84:1, unique), tall ridge on lateral ethmoid for contact with metapterygoid (97:2), mesethmoid flares anteriorly (102:1), eight or more dorsal-fin rays (142:1), nuchal plate covered by skin or plates (147:1, nuchal plate may be exposed and supporting odontodes in nuptial male Dolichancistrus), reversal to a large space between posterior process of coracoid strut and posterior process of coracoid (164:0), reversal to tall ventral ridge of pelvic basipterygium (172:0), and widened first (unbranched) ray of pelvic fin (177:1, reversed in Dolichancistrus).

Comparative diagnosis. Chaetostomatini can be separated from all other Hypostominae except Acanthicini, Collosimystax new genus, and Pterygoplichthysby having eight or more branched dorsal-fin rays (vs. seven); from Acanthicini and Pterygoplichthys by lacking elongate patches of sharp odontodes on lateral plate keels (most species lack lateral plate keels entirely, Andeancistrus platycephalus and Chaetostoma spondylus have round patches of elevated, keel-like odontodes on lateral plates); from Collosimystax new genus by mature males having usually zero and maximally two cheek odontodes extending past the head (vs. >40), and by having plates in ventral series posterior to anal fin broadly convex (vs. dorsal halves of plates concave, forming a strong keel); and from Pterygoplichthys by lacking plates on abdomen (vs. abdominal plates present), and by having caudal fin truncate or maximally emarginate (vs. forked).

Geographical distribution. Most species with exclusively Andean distribution, including cis-Andean streams from southern Peru to the Caribbean Andes west of Caracas (including the Caribbean slope) and trans-Andean basins from the Tumbes River in Northern Peru to the Chagres River of Panamá. Three species of Chaetostoma occur in scattered drainages east of the Andes, such as the Caroni, Caura, and Branco rivers draining the Guiana Shield north in Venezuela and south in Brazil, and a few northern and southern tributaries of the lower Amazon in Brazil (Meza-Vargas et al., 2022).

Tribe Hypostomini Kner, 1853

Included genera.

‘Hemiancistrus’ chlorostictus group (Armbruster et al., 2015).

Hypostomus, Lacépède, 1803:144. Type-species: Hypostomus guacari Lacépède, 1803. Synonyms: Cheiridodus Eigenmann, 1922, Cochliodon Heckel, 1854 (in Kner, 1854), Plecostomus Gronow 1763, and Watawata Isbrücker & Michels, 2001 (in Isbrücker et al., 2001).

Pterygoplichthys, Gill, 1858:408. Type-species: Hypostomus duodecimalis Valenciennes, 1840 (in Cuvier, Valenciennes, 1840). Synonyms: Glyptoperichthys Weber, 1991 and Liposarcus Günther, 1864.

Phylogenetic diagnosis. No unambiguous character states were found to support Hypostomini.

Comparative diagnosis. Hypostomini contains most of the large, stout-bodied loricariids, but these can be difficult to distinguish from other Hypostominae except by genus or species group. Hypostomus (with the exception of H. cerrado) differs from all other Hypostomini as well as all other tribes (except Corymbophanes of the Ancistrini, Aphanotorulus, Isorineloricaria, and Peckoltia relictum of the Peckoltini, and Spectracanthicus murinus of the Spectracanthicini) by having the cheek plates evertible to only about 30° from the head and lacking hypertrophied odontodes (vs. 75°+ from the head and having hypertrophied odontodes; Pseudancistrus have hypertrophied cheek odontodes, but cannot evert their cheek odontodes beyond 30°); from Corymbophanes by having either an adipose fin or fin completely missing without replacement by azygous plates (vs. adipose fin replaced by postdorsal ridge of raised azygous plates) and by having an iris operculum (vs. iris operculum absent); from Aphanotorulus and Isorineloricaria by lacking hypertrophied odontodes on the lateral trunk plates of nuptial males (vs. lateral plates and/or caudal-fin spines covered in large odontodes in nuptial males), by generally being brown with black spots or saddles or dark gray with light spots (Hypostomus yaku is uniformly brown, Martins et al., 2014) (vs. almost white to light tan with black spots); and by having a small buccal papilla (vs. single large or many small buccal papillae); from Peckoltia relictum by completely lacking hypertrophied cheek odontodes (vs. very small cheek odontodes); and from S. murinus by having dorsal fin free from adipose (vs. posterior membrane of dorsal fin expanded, entirely adnate to body reaching adipose-fin spine).

Pterygoplicthys can be separated from all other Hypostominae except Acanthicini, Chaetostomatini, and Colossimystax by having nine to 14 dorsal-fin rays (vs. seven); from Acanthicini by having relatively weak lateral plate keels and associated odontodes (vs. strong/sharp), by having odontodes evenly distributed across lateral plates (vs. odontodes reduced above and below keel rows), and by having a weaker ability to evert cheek-odontodes; and from Chaetostomatini and Colossimystax by having elongate lateral plate keels (vs. keels absent or with rounded clusters of odontodes in Andeancistrus platycephalus and Chaetostoma spondylus Salcedo & Ortega, 2015) and by having plates on the abdomen (vs. plates absent). Hypostomus cerrado and the ‘Hemiancistrus’ chlorostictos group have evertible cheek plates with hypertrophied odontodes.

Hypostomus cerrado can be separated from most other Hypostominae tribes by having weak lateral plate keels and a distally expanded pectoral-fin spine forming a club-like structure in adults (vs. no lateral plate keels in most other tribes or very strong keels and associated odontodes in Acanthicini and no expansion of the pectoral-fin spine). The ‘Hemiancistrus’ chlorostictos group can be separated from Ancistrus, Araichthys, Corymbophanes, Dekeyseria, Lasiancistrus, Neblinichthys,and Pseudolithoxus by having five rows of plates on the caudal peduncle (vs. three); from Ancistomus by either being almost black with white spots or tan with black spots (vs. gray with black spots); from Aphanotorulus and Isorineloricaria by either being almost black with white spots or tan with medium black spots (vs. very light gray or tan with small black spots), by nuptial males lacking hypertrophied odontodes on lateral plates (vs. nuptial males with hypertrophied odontodes dense and widespread on lateral plates, especially caudally), from Aphanotorulus by having a small buccal papilla (vs. buccal papilla large or numerous and widespread); from Baryancistrus,‘Baryancistrus’, Parancistrus,and Spectracanthicus, by having a small posterior membrane of the dorsal fin (vs. posterior membrane of dorsal fin expanded, reaching the adipose-fin spine in all except B. longipinnis); from Panafilus, Panaqolus, Panaque,many Peckoltia, Peckoltichthys, Pseudoqolus,and Scobinancistrus by having dentaries long and forming an oblique angle with many small teeth (vs. dentaries short and forming an acute angle with fewer, larger teeth) and from remaining Peckoltia by being either almost black with white spots or tan with large black spots (vs. with dorsal saddles, with very large dark spots, being almost colorless, or having a golden tan background color with no spots); from ‘B.’ demantoides, ‘H.’ guahiborum, and ‘H.’ subviridis by lacking a light edge to the dorsal and/or caudal fins (vs. yellow or orange bands along edges of dorsal and/or caudal fins).

Geographical distribution. Hypostomini is broadly distributed across cis-Andean South American drainages from the La Plata River northward (including Trinidad), and trans-Andean drainages from northern Ecuador to the Terraba River of Costa Rica (extending further into Central America than any other loricariid lineage). Introduced populations of mainly Pterygoplichthys but also Hypostomus are found in tropical and subtropical regions around the world.

Tribe Lithoxini Isbrücker, 1980

Included genera.

Avalithoxus Lujan et al., 2018:10. Type-species: Lithoxus jantjae Lujan, 2008

Lithoxus, Eigenmann, 1910:405. Type-species: Lithoxus lithoides Eigenmann, 1912.

Exastilithoxus Isbrücker, Nijssen in Isbrücker, 1979:88. Type-species: Pseudacanthicus (Lithoxus) fimbriatus Steindachner, 1915.

Paralithoxus, Boeseman, 1982:46. Type-species: Ancistrus bovallii Regan, 1906.

Phylogenetic diagnosis. Reversal to a short, narrow accessory process of the first ceratobranchial (7:1, 8:1), reversal to a narrow fifth ceratobranchial (10:0), loss of the accessory process on the first epibranchial (14:0), loss of the posterior shelf on the fourth epibranchial (17:0), reversal to a narrow hypohyal (20:0), an elongate first hypobranchial (23:1), reversal to the anterohyal being located on or behind the hyomandibula (26:0), reversal to a round upper pharyngeal jaw with evenly distributed teeth (30:0), lateral wall of posterohyal absent so that posterohyal forms a half cylinder (32:1), reversal to no mesial contact of hyomandibula and quadrate (33:0), posterior portion of hyomandibula forming a shelf dorsally such that suture to pterotic-supracleithrum is nearly perpendicular to preoperculo-hyomandibular ridge (40:1), posterior process of hyomandibula incorporated into main body of hyomandibula (41:1, unique), branched preoperculo-hyomandibular ridge (48:1), reversal to loss of metapterygoid channel and dorsal surface of the metapterygoid being only slightly split, forming a narrow channel (52:1, 53:0), dentary tooth rows forming acute angle (69:0), maxilla expanded ventrally (71:1), bar-shaped opercle (75:2), two to four plates between canal plate and opercle (88:2), reversal to small mesethmoid disk (100:1), wide ventral process of sphenotic (116:1), bifid hemal spines (122:1), first neural spine anterior to first dorsal-fin pterygiophore (125:1), tip of transverse process of Weberian complex centrum not contacting compound pterotic (135:1), reduction of exposed portion of cleithral process (157:1), reversal to large space between posterior process of coracoid strut and posterior process of cleithrum (164:0), curved anterolateral processes of basipterygium meeting or nearly meeting at midline (167:0), loss of posteroventral ridge of basipterygium (173:0), enlarged teeth (205:2).

Comparative diagnosis. The Lithoxini can be separated from all except Leporacanthicus by having a nearly round, flat oral disk with mandibular barbels located and directed anterolaterally (vs. lips oval and mandibular barbels located and directed posterolaterally) and from Leporacanthicus by having more than two premaxillary teeth and all teeth of similar length (vs. two teeth per premaxilla and premaxillary teeth much longer than dentary teeth; see Lujan et al., 2018, for more detail).

Geographical distribution. Lithoxini is distributed exclusively within the Guiana Shield, from right bank tributaries of the Orinoco River, to the upper Negro and Branco rivers, to north-flowing basins from the Essequibo eastward to the Oyapock, and drainages flowing south from the Guianas into the lower Amazon.

Tribe Peckoltini, new tribe

urn:lsid:zoobank.org:act:C1105224-245D-4807-A57A-C91C39D34EDC

Included genera.

Ancistomus Isbrücker, Seidel in Isbrücker et al., 2001:17. Type-species: Ancistrus snethlageae Steindachner, 1911.

Aphanotorulus Isbrücker, Nijssen, 1983:105. Type-species: Aphanotorulus frankei Isbrücker & Nijssen, 1983 (synonym of A. unicolor (Steindachner, 1908)). Synonym: Squaliforma Isbrücker & Michels, 2001 (in Isbrücker et al., 2001).

‘Baryancistrus’ beggini Lujan, Arce, Armbruster, 2009:51.

‘Baryancistrus’ demantoides, Werneke, Sabaj Pérez, Lujan, Armbruster, 2005a:535.

‘Hemiancistrus’ guahiborum, Werneke, Armbruster, Lujan, Taphorn, 2005b:544.

‘Hemiancistrus’ landoni group (includes ‘H.’ landoni Eigenmann, 1916 (with ‘H.’ hammarlundi Rendahl, 1937 as a synonym) and ‘H.’ furtivus Provenzano & Barriga Salazar, 2017).

‘Hemiancistrus’ subviridis Werneke, Sabaj Pérez, Lujan, Armbruster, 2005a:538.

Hypancistrus Isbrücker, Nijssen, 1991:347. Type-species: H. zebra Isbrücker & Nijssen, 1991. Synonym: Micracanthicus Lujan & Armbruster, 2011.

Isorineloricaria Isbrücker, 1980:15. Type-species: Plecostomus spinosissimus Steindachner, 1880.

Panafilus Lujan et al., 2017:332. Type-species: Panaque albomaculatus Kanazawa, 1958.

Panaqolus Isbrücker, Schraml, in Isbrücker et al., 2001:20. Type-species: Panaque gnomus Schaefer & Stewart, 1993. With three subgenera (Panafilus, Panaqolus and Panaqoco per Lujan et al., 2017).

Peckoltia, Miranda Ribeiro, 1912:1912. Type-species: Chaetostomus vittatus Steindachner, 1881. Synonym: Etsaputu, Lujan, Armbruster & Rengifo, 2011.

Peckoltichthys, Miranda Ribeiro, 1917:49. Type-species: Peckoltichthys filicaudatus Miranda Ribeiro, 1917 (synonym of Chaetostomus bachi Boulenger, 1898). Synonym: Sophiancistrus Isbrücker & Seidel, 2001 (in Isbrücker et al., 2001).

Pseudoqolus Lujan et al., 2017:333. Type-species: Panaqolus koko Fisch-Muller, Covain, 2012 (in Fisch-Muller, Montoya-Burgos, le Bail, Covain, 2012).

Scobinancistrus Isbrücker, Nijssen, 1989:542. Type-species: Scobinancistrus pariolispos Isbrücker & Nijssen, 1989.

‘Spectracanthicus’ immaculatus Chamon, Rapp Py-Daniel, 2014:12.

Phylogenetic diagnosis. No unambiguous character states were found to support Peckoltini.

Comparative diagnosis. Peckoltini is a diverse group of genera not easily separated as a group from other members of the Hypostominae. Peckoltini genera tend to have hypertrophied odontodes on lateral plates, especially along the caudal peduncle, while this character is not seen in other Hypostominae; however, these hypertrophied caudal trunk odontodes are also unknown or presumed absent in some species of Peckoltini. Of Peckoltini genera, only Ancistomus lacks a recent taxonomic review, and it is largely separated from all other Hypostominae by having a gray head and body base color with black spots (vs. base color, white, tan, brown, or black).

Geographical distribution. Peckoltini is widely distributed throughout the Amazon, Orinoco, Essequibo and other coastal basins of the Guianas as well as the trans-Andean Guayas and Esmeraldas drainages in Ecuador, the Magdalena River, and the Lake Maracaibo basin.

Tribe Pseudancistrini, new tribe

urn:lsid:zoobank.org:act:CE2CF701-3692-40FF-A9FE-D926399A8807

Included genera.

Pseudancistrus Bleeker, 1862:2. Type-species: Hypostomus barbatus Valenciennes, 1840 (in Cuvier, Valenciennes, 1840).

Phylogenetic diagnosis. With Pseudancistrus megacephalus, Pseudancistrini is diagnosed by hyomandibula contacting only the compound pterotic (no prootic contact; 35:0>1), walls of metapterygoid channel tall (56: 0>1), straight, spoon-shaped anterior process on metapterygoid (58: 0>1, shared with Stellantini), sphenotic lacking external contact with posteriormost infraorbital (117: 0>1).

All taxa except P. megacephalus are diagnosed by: anterohyal greatest width greater than half length (1: 0>1), hyomandubula deflected beyond posterior margin such that posterior margin is visible when mesial surface of hyomandibula is viewed (46: 0>1), almost vertically-oriented preopercle (61: 1>0), reduction in gap between anterior process of compound pterotic and main body (111: 2>1), forward extension of anterior process of compound pterotic halfway or greater through orbit (112: 0>1), distal margin of rib of sixth vertebral centrum flared distally such that tip is wider than shaft (128: 0>1), reversal to moderately evertible cheek plates (184: 2>1), hypertrophied odontodes along snout margin (188: 0>1), sheaths of snout odontodes long and well separated from odontode, forming tentacules (208: 0>1).

Comparative diagnosis. Pseudancistrini (except P. megacephalus) differs from most other Hypostominae except Corymbophanes, Cryptancistrus Fisch-Muller, Mol & Covain, 2018, some Guyanancistrus Isbrücker, 2001 (in Isbrücker et al., 2001), Hopliancistrus, Lithoxancistrus Isbrücker, Nijssen & Cala, 1988, Neblinichthys Ferraris, Isbrücker & Nijssen, 1986,and Pseudolithoxus by having hypertrophied odontodes along snout margin of nuptial males; from Corymbophanes by having hypertrophied, evertible cheek odontodes (vs. no evertible cheek odontodes); from Cryptancistrus, Guyanancistrus,and Hopliancistrus by having snout odontodes evenly arranged along entire snout margin and thin (vs. only at anterolateral corners and thick); from Araichthys, Corymbophanes,and Neblinichthys (and maybe Paulasquama and Yaluwak Lujan, Armbruster in Lujan et al., 2019) by lacking hypertrophied odontodes on top of snout; from Lithoxancistrus and Colossimystax by lacking enlarged papillae behind dentary teeth); and from Stellantini by having slight keel on midventral plate row on caudal peduncle, with dorsal laminae of plates largely flat (vs. plates strongly keeled with dorsal laminae strongly convex).

Geographical distribution. Found in north-flowing drainages of the eastern Guiana Shield from the Caroni and Essequibo basins east to the Oyapock, the south-flowing Branco, Negro, and Trombetas drainages, more eastward northern tributaries of the lower Amazon, and the Tapajós and Xingu rivers draining the northern Brazilian Shield.

Remarks. Placement of P. megacephalus in Pseudancistrus is uncertain, thus the phylogenetic diagnosis above is provided with and without P. megacephalus. Pseudancistrus megacephalus has a deeper body than congeners, lacks hypertrophied odontodes along the snout, and the skull (Fig. 4) contains significant differences. These include the posterior shelf of the pterotic being largely parallel with the main body of the hyomandibula in P. megacephalus (vs. bent medially), the anterior process of the pterotic being longer and more separated from the main body of the pterotic, and the lateral wall of the pterygoid channel being differently shaped. The orientation of the suspensorium (turquoise in Fig. 4, also indicated) forms almost a right angle at the posteroventral corner when viewed laterally (vs. forming almost a straight line), the preopercle lacks a process for articulation with the canal plate (vs. process present; the canal plate is the fulcrum for rotation of the evertible cheek odontodes), and the metapterygoid condyle to the suspensorium is tall (vs. short). Pseudancistrus megacephalus has not been collected within its range in Guyana and Suriname since 1909 despite several fairly intensive collecting efforts, suggesting it may be either regionally extirpated or extinct (Armbruster, 2023a). The MBUCV collection has five lots and 19 specimens identified as Pseudancistrus megacephalus from the Cuyuni River in Venezuela, all collected in 1987 and 1991. Thus the Cuyuni may remain a refuge, although it has suffered from even worse mining impacts than other parts of the species’ range.

Tribe Spectracanthicini Isbrücker & Nijssen, 1989

Type-genus. Sepctracanthicus Nijssen & Isbrücker, 1987

Included genera.

Baryancistrus Rapp Py-Daniel, 1989:245. Type-species: Hypostomus niveatus Castelnau, 1855. See Rapp Py-Daniel et al. (2011).

Hemiancistrus Bleeker, 1862:2. Type-species: Ancistrus medians Kner, 1854. See Fisch-Muller et al. (2012) and Armbruster et al. (2015).

Parancistrus Bleeker, 1862:2. Type-species: Hypostomus aurantiacus Castelnau, 1855. See Rapp Py-Daniel (1989) and Rapp Py-Daniel, Zuanon (2005). Synonym: Acanthodemus Marschall, 1873.

Spectracanthicus Nijssen, Isbrücker, 1987:93. Type-species: Spectracanthicus murinus Nijssen & Isbrücker, 1987. See Rapp Py-Daniel (1989) and Chamon, Rapp Py-Daniel (2014).

Phylogenetic diagnosis. Posterior region of hyomandibula deflected mesially causing opercle to sit at almost right angle to main body axis (42:1), opercle not supporting odontodes (79:1), and curved anterolateral processes of basipterygium that meet or nearly meet at midline (167:0).

FIGURE 4 |
µCT renderings of the crania of A.Pseudancistrus megacephalus,BMNH 1978.9.12.3, and B.P. barbatus, ROM86176, in slightly anterolateral (top) and ventral views (bottom) emphasizing major differences between P. megacephalus and Pseudancistrus sensu stricto. CPP: canal plate process, HS: Hyomandibula posterior shelf, LPC: Lateral wall of the pterygoid channel, MPC: metapterygoid condyle, PAP: compound pterotic anterior process, SUSP: suspensorium.

Comparative diagnosis. Spectracanthicini cannot be separated from all other hypostomines as a group. Baryancistrus, ‘B.’ beggini, ‘B.’ demantoides, Parancistrus, and Spectracanthicus can be separated from all except ‘Spectracanthicus’ immaculatus of the Peckoltini by having a fully adnate dorsal fin and a posterior extension of the dorsal-fin membrane that reaches either the adipose fin or at least two plates posterior to the insertion of the posteriormost dorsal-fin ray (vs. posterior dorsal-fin membrane maximally extending one plate from the insertion of the posteriormost dorsal-fin ray and never reaching adipose fin); all of these except‘B’. beggini can be separated from ‘S.’ immaculatus by having light spots (vs. solid gray or black). Hemiancistrus medians can be separated from all other hypostomines except the Acanthicini by having all odontodes on the head and lateral plates arranged in lines (vs. scattered) and from the Acanthicini by having many very small odontodes in lines (vs. very few, fairly large odontodes) and by having seven dorsal-fin rays (vs. eight to 10). Some Baryancistrus,‘B.’ demantoides,‘H.’ guahiborum,and ‘H.’ subviridis can be separated from most other Hypostominae by having a light-colored (white, yellow, or orange) margin to the dorsal fin.

Tribe StellantiniArmbruster & Lujan, new tribe

urn:lsid:zoobank.org:act:1D1E1710-3653-4CFA-A6BB-1975401D6ADF

(Fig. 1; Tabs. 1 and S3)

Type-genus. Stellantia, new genus

Included genera.

Colossimystax, new genus

Stellantia, new genus

Phylogenetic diagnosis. Hyomandibula contacting prootic (0>1), posteromedial invagination of ceratobranchial 5 (11: 0>1), straight, spoon-shaped anterior process on metapterygoid (58: 0>1, shared with Pseudancistrini), forward extent of anterior process of compound pterotic long, halfway through orbit or greater (112: 0>1), and straight anterolateral processes of pelvic basipterygium (167: 1>2). In addition, Stellantini uniquely possesses plates along ventral series on the caudal peduncle that are strongly bent to form a keel with the keel accentuated by having the dorsal lamina of the plates strongly concave.

Comparative diagnosis. Morphometric data reported in Tab. 1.The two species of Stellantini are dramatically different from one another, but the tribe can be identified from other Hypostominae by having a strong keel on the ventral plate series on the caudal peduncle made by the ventral lamina of each plate being strongly convex and the dorsal lamina of each plate being strongly concave (vs. maximally having a slight keel made predominantly of odontodes and the dorsal lamina of each ventral plate being flat to very slightly concave).

Geographical distribution. Both species of Stellantini are found in main channels of the upper Orinoco and Negro river basins, including the Casiquiare River, in Venezuela, Colombia, and possibly also northernmost Brazil, though no Brazilian specimens have been observed or reported (Fig. 5).

FIGURE 5 |
Distribution of Colossimystax pectegenitor (black dots) and Stellantia siderea (white dots).

ColossimystaxArmbruster & Lujan, new genus

urn:lsid:zoobank.org:act:3F6C7DC3-24AC-4BE2-8D7F-BE77FC4CAAD5

(Figs. 1A, 2C)

Type-species. Pseudancistrus pectegenitor Lujan, Armbruster & Sabaj Pérez, 2007

Included species.

Pseudancistrus pectegenitor Lujan, Armbruster, Sabaj Pérez, 2007:164, figs. 1b, 2-3. Río Casiquiare, 73 kilometers northeast of San Carlos de Río Negro, 02.3525°, -066.5753°, Amazonas, Venezuela.

Phylogenetic diagnosis. Spindle-shaped hypohyal (21: 0>1), upper pharyngeal jaw with invagination in shelf (29: 0>1), reversal to horizontally oriented preopercle (61: 1>0), wide, blunt articulating condyle of quadrate (67: 0>1), tall ridge on lateral ethmoid for contact with metapterygoid (97:2), reduction to three to eight vertebrae from first normal neural spine posterior to dorsal fin to spine under preadipose plate (120: 1>0; this is concomitant with a unique shortening of the body posterior to the dorsal fin), flared distal margin of rib of sixth vertebral centrum (128: 0>1), ten dorsal-fin rays (142: 0>1), reduction to five or six dorsal-fin radial elements with transverse processes (145: 1>0), reversal to wide posterior process of coracoid (158: 2>1), presence of dentary papillae (180: 0>1), presence of tentacules on hypertrophied snout and pectoral-fin spine odontodes, tentacules shorter than associated odontodes (208: 0>1, 209: 0>1). Further, Colossimystax has a larger supraoccipital crest than Stellantia or other species currently or formerly in Pseudancistrus, with crest most similar to Hemiancistrus medians but still taller and with a greater ventromedial lamina (Fig. 6).

TABLE 1 |
Morphometrics and counts for species of Stellantini.

	Colossimystax pectegenitor (N = 4)			Stellantia siderea (N = 17)
Measurement	Range	Mean	SD	Range	Mean	SD
Standard length (mm)	173.6–241.6	216.8	–	110.7–183.0	155.4	–
Percentages of standard length
Predorsal length	42.0–44.2	43.5	1.0	37.2–39.0	38.1	0.5
Head length	35.9–38.1	37.0	0.9	29.4–31.7	30.7	0.6
Head-dorsal length	5.6–6.8	6.2	0.6	6.9–8.3	7.7	0.4
Cleithral width	29.2–34.1	31.4	2.1	25.1–28.2	26.4	0.9
Head-pectoral length	30.6–32.9	31.9	1.2	24.2–26.8	25.7	0.8
Thorax length	22.9–25.1	24.0	1.0	20.3–25.0	22.8	1.1
Pectoral-spine length	38.3–42.2	40.1	1.9	25.5–32.1	27.9	1.4
Abdominal length	22.3–24.7	23.5	1.0	21.4–23.7	22.7	0.7
Pelvic-spine length	23.1–27.4	24.7	2.0	21.3–24.9	23.5	1.0
Postanal length	27.8–31.5	29.5	1.5	33.5–37.4	36.1	1.0
Anal-fin spine length	11.2–13.3	12.2	1.0	6.9–10.4	8.0	0.9
Dorsal-pectoral distance	24.6–26.4	25.7	0.8	22.7–24.2	23.6	0.5
Dorsal spine length	27.7–35.2	31.3	3.6	28.0–39.9	34.0	3.3
Dorsal-pelvic distance	22.6–25.5	23.9	1.5	17.1–21.9	20.5	1.1
Dorsal-fin base length	34.0–38.0	35.6	1.8	23.7–28.4	25.9	1.2
Dorsal-adipose distance	8.8–11.1	10.2	1.0	16.7–19.5	18.4	0.8
Adipose-spine length	5.6–7.8	6.6	1.1	6.3–9.6	8.5	0.8
Adipose-up. caudal distance	8.9–10.5	9.6	0.8	11.9–17.3	14.1	1.5
Caudal peduncle Dp.	12.1–13.6	12.7	0.7	7.5–9.2	8.4	0.4
Adipose-low. caudal distance	17.4–18.5	17.8	0.5	19.1–23.0	20.7	1.0
Adipose-anal distance	18.9–20.5	19.8	0.7	18.6–21.7	20.5	0.8
Dorsal-anal distance	14.4–16.4	15.5	0.9	11.7–13.8	13.0	0.5
Pelvic-dorsal distance	30.0–34.8	32.3	2.5	23.8–27.2	25.1	1.0
Percentages head length
Head-eye length	25.3–29.9	27.5	1.9	27.5–36.2	30.5	2.7
Orbit diameter	14.6–16.0	15.0	0.6	15.0–18.1	16.5	0.9
Snout length	66.1–69.1	68.0	1.4	63.0–70.6	66.8	2.0
Internares width	11.0–12.2	11.4	0.5	9.6–12.9	10.9	1.0
Interorbital width	33.0–41.7	36.8	3.6	34.4–49.0	42.0	5.0
Head Dp.	62.8–64.4	63.4	0.7	61.4–68.2	63.8	1.7
Mouth length	49.4–58.4	52.3	4.1	48.4–58.5	52.8	2.6
Mouth width	62.3–75.9	70.3	6.2	59.9–72.7	65.5	2.8
Barbel length	9.3–10.9	10.1	0.8	3.2–8.2	6.2	1.4
Dentary tooth cup length	23.0–27.2	24.8	1.8	21.0–25.5	23.3	1.5
Premax. tooth cup length	21.5–26.5	24.5	2.2	20.4–25.5	23.3	1.6
Counts	Range	Median		Range	Median
Plates in median row	24.0–24.0	24.0		25–25	25
Plates in inframedian row	23.0–23.0	23.0		24–25	24
Plates in supramedian row	24.0–25.0	24.0		25–26	25.0
Dorsal-fin rays	I,10–I,11	I,10		I,7–I,7	I,7
Pectoral-fin rays	I,6–I,6	I,6		I,6–I,6	I,6
Pelvic-fin rays	i,5–i,5	I,5		i,5–i,5	i,5
Anal-fin rays	i,5–i,5	I,5		i,4–i,4	i,4
Caudal -fin rays	i,13,i–i,14,i	i,14,i		i,14,i–i,14,i	i,14,i
Dentary teeth	126–134	128		63–102	81
Premaxillary teeth	119–164	131		65–113	84

Comparative diagnosis. Colossimystax is readily distinguished from all other Hypostominae except Acanthicini, Chaetostomatini,and Pterygoplichthys by having 10 dorsal-fin rays (vs. 7); from all other Hypostominae except Stellantia by having the dorsal lamina of each ventral plate of the caudal peduncle concave, accentuating the ventrolateral keel of the caudal peduncle (vs. ventral plates on caudal peduncle lacking strongly concave dorsal lamina or plates rounded and keel absent); from other species with more than seven dorsal-fin rays except Dolichancistrus by nuptial males having hypertrophied cheek odontodes reaching to at least the edge of the third plate of the midventral series (vs. maximally reaching the first plate); from Dolichancistrus by nuptial males having many hypertrophied cheek odontodes (vs. 1 or 2); from Hypostominae except Chaetostoma and Lithoxancistrus by having a single or small cluster of enlarged papillae located medially on dentaries interior to tooth rows (vs. all papillae small).

Description. See Tab. S3 and Lujan et al. (2007).

Geographical distribution. Found in main channels and major tributaries of the Orinoco River upstream of San Fernando de Atabapo and in the Casiquiare River above its confluence with the Negro River, including the lower Ventuari River. Currently known exclusively from Venezuela but may also occur in neighboring basins of Colombia and Brazil (Fig. 5).

Etymology. Colossimystax is fromthe Latin colossicon for gigantic and mystax for moustache in reference to the very long cheek odontodes that look like a moustache, a masculine noun.

Conservation status. Colossimystax pectegenitor was evaluated as Least Concern (LC) by the IUCN (Echevarría, 2019). Only three disjunct localities are known, but all are main channel habitats, suggesting a likely contiguous distribution throughout a remote area of southern Venezuela in which the most threatening impact is gold mining.

Material examined. Amazonas, Venezuela. Holotype: MCNG 54797 [ex AUM 42130], 241.6 mm SL, Río Casiquiare. Paratypes: ANSP 182801 [ex AUM 42181], 1, 225.1 mm SL, Río Orinoco; AUM 42202, 1, 227.0 mm SL, Río Casiquiare; AUM 43192, 1 c&s, 173.6 mm SL, Río Orinoco.

FIGURE 6 |
µCT renderings of neurocrania (left, lateral view) of A.Hemiancistrus medians, ANSP 187122, B.Pseudancistrus barbatus, ROM 86176, C.Colossimystax pectegenitor, AUM 42130, D.Stellantia siderea, AUM 54310, E.Lithoxancistrus coquenani, AMNH 91025, F.Lithoxancistrus yekuana, AUM 39473. Scale bars = 1 cm.

StellantiaArmbruster & Lujan, new genus

urn:lsid:zoobank.org:act:894AA6EB-3851-4EA7-B4FB-24724F2A0491

(Figs. 1B, 2B)

Type-species. Pseudancistrus sidereus Armbruster, 2004b

Included species.

Pseudancistrus sidereus Armbruster, 2004b:8, fig. 3. Río Siapa from 10–15 kilometers downstream, Río Casiquiare - Río Negro drainage, 01.50000°, -065.71667°, Río Orinoco drainage, Amazonas, Venezuela.

Phylogenetic diagnosis. Reversal to large interhyal (27: 1>0), tall walls of metapterygoid channel (56: 0>1), reversal to narrow quadrate (64: 1>0), loss of flap of quadrate extending below symplectic foramen (66: 1>0), reversal to two to four cheek plates between canal plate and opercle (88: 3>2); no contact between infraorbital 4 and orbit (90: 1>2), anterior margin of mesethmoid flared (102: 0>1), loss of exterior contact between sphenotic and posteriormost infraorbital (117: 0>1), and increase in number of vertebrae to 12–15 from first normal neural spine posterior to dorsal fin up to and excluding the hypural (121:1).

Comparative diagnosis. Stellantia is readily identified from all other Hypostominae except Colossimystax by having the dorsal lamina of each ventral plate of the caudal peduncle concave, accentuating the caudal peduncle keel (vs. caudal peduncle ventral plates rounded, lacking concave dorsal lamina, caudal peduncle keel weak or absent); and from Colossimystax by having seven branched dorsal-fin rays (vs. 10).

Geographical distribution. Known from main channels of the upper Orinoco River basin upstream of San Fernando de Atabapo, including the lower Ventuari River, and the Casiquiare River basin upstream of its confluence with the Negro River, including the lower Siapa River, exclusively in Amazonas, Venezuela.

Description. See Tab. S3 and Armbruster (2004b).

Etymology. An abstract, feminine noun modified from the Latin adjective stellans for starry in reference to the dark body with white to yellow spots which appear like a field of stars, a feature that inspired the species epithet as well. Stellantia requires a change of ending for the single species in the genus: Stellantia siderea.

Conservation status. Stellantia siderea was evaluated as Least Concern (LC) by the IUCN (Armbruster, 2023b). The species is common throughout its range.

Material examined. Río Orinoco drainage, Amazonas, Venezuela. Holotype: MCNG 26125, 175.6 mm SL, Paratypes: AUM 37562, 1, 148.7 mm SL; FMNH 105294, 4, 149.5–176.7 mm SL; MCNG 48261, 1 c&s, 149.8 mm SL.

DISCUSSION

We present a new tribe-level taxonomy for the Hypostominae based on multiple genetic studies published over several decades. The first DNA-based hypotheses on Loricariidae interrelationships were those of Montoya Burgos et al. (1997, 1998), and the results of those studies have been largely confirmed in subsequent molecular analyses including more markers and taxa (Lujan, 2015a; Roxo et al., 2019). These results suggest that previous morphology-based phylogenetic studies (Schaefer, 1986; Armbruster, 2004a, 2008) are significantly biased by morphological homoplasy and, as the present study shows, rapid character evolution. The homoplastic presence and degree of development of a cheek odontode eversion mechanism driven by an anteroventral, lever-like process of the opercle has been a large source of this bias. This mechanism is unique to the Hypostominae, and it is easy to imagine how earlier research might have been biased by the assumption that such a complex structure is a derived state that is rarely lost.

Armbruster (2004a) described a transitional series in the complexity or degree of the cheek odontode eversion mechanism across Loricariidae, from no eversion (184:0; all but Hypostominae), to slight eversion (184:1; Hypostomus, Pterygoplichthys), to strong eversion (184:2). The opercle, which is the central bone of this mechanism, varies from a primitive triangular shape (75:0), to sickle-shaped (75:1), to bar-shaped (75:2) with the sickle shape considered intermediate. When applied at the scale of a clade as diverse as Loricariidae, morphology-based phylogenetics requires diverse and continuously variable morphologies to be binned into an arbitrarily small number of character states. The opercles representing Hemiancistrus and species now or formerly in Pseudancistrus (all sickle-shaped) illustrate the complexity of form that must be collapsed into a single state (Fig. 7). Some species with highly evertible cheek plates have correlated modifications of the hyomandibula (37:1, 39:1, 40:1, 41:1, 42:1, 76:1), the quadrate articulating with the canal plate or other parts of the suspensorium (65:1, 85:1), increased fragmentation of the cheek plates (88:3) as well as other characters that influence or are influenced by cheek odontode evertibility. Such a functionally interrelated complex of characters easily overwhelms the phylogenetic signal from other characters, which are conversely too few and poorly correlated to correct the consequent bias.

DNA-based phylogenies show that many of the derived characters related to cheek odontode eversion occurred early in Hypostominae evolution and were lost or regained multiple times throughout the evolutionary history of the subfamily. Given the dominance of these characteristics, many clades lack morphological synapomorphies when the characters of Armbruster (2004a) are mapped onto the compound molecular phylogeny. While the molecular phylogeny could provide a fruitful foundation for the discovery of new characters to support such clades, it would be difficult to amass the specimens needed and it is beyond the scope of this study. The use of computed tomography to generate and archive three-dimensional digital libraries of skeletal morphology is accelerating our ability to compare individual bones in multiple standardized perspectives (Fig. 7). The near instant accessibility to such imagery allows for easier and more thorough assessments of character states than was ever historically possible using cleared and stained or dry skeletal material. Although molecular phylogenies are more likely to give results closer to the true tree than morphological phylogenies, future systematists will need to examine morphology in much greater detail, benefitting from new technologies, to truly understand character evolution in the Loricariidae.

Here we describe the new tribe Pseudancistrini for species once ascribed to Pseudancistrus sensu stricto. Armbruster (2004b) had recognized a broader Pseudancistrus; however, genetic evidence shows that this was in error, with several taxa once part of Pseudancistrus, such as Collosimystax, Lithoxancistrus, Guyanancistrus, and Stellantia, being removed from Pseudancistrus in recent studies. Most of the taxa removed from Pseudancistrus share with Pseudancistrus the presence of hypertrophied odontodes along the side of the head; however, this is a common trait across Loricariidae. Of the species now recognized in Pseudancistrini, Pseudancistrus megacephalus is the most curious, morphologically distinct, and ambiguous in its relationship to other species. This species has not been collected in its historical range in Guyana and Suriname in over 100 years and no genetic samples are currently available, thus we cannot test our taxonomic hypothesis with genetic data. We therefore define Pseudancistrini using distinct sets of character states that would be relevant whether P. megacephalus is included in Pseudanctrini or excluded.

We conclude this tribe-level reclassification of subfamily Hypostominae by erecting the new tribe Stellantini for two species from the upper Orinoco and Negro River drainages that are strongly supported as a clade in Lujan et al. (2015a). The phylogenetic position of Stellantini in Lujan et al. (2015a) is similar to that in the genomic analysis of Roxo et al. (2019), being one of four lineages (Ancistrini, Lithoxini, Pseudancistrini, Stellantini) that branch off after Chaetostomini but before the consistently supported crown-clade of Acanthicini + (Spectracanthicini + (Hypostomini + Peckoltini)), and whose interrelationships are weakly resolved in both studies. Nonetheless, both these studies and Covain, Fisch-Muller’s (2012) phylogenetic analysis of Pseudancstrius sensu lato, found Stellantini to be more closely related to tribes other than Pseudancistrini, supporting our recognition of this clade as new. With the two Stellantini species so vastly different from one another, splitting them into two monotypic genera seems to be the best solution as there is very little to outwardly suggest that they are closely related except for the modified caudal peduncle keel.

FIGURE 7 |
µCT renderings of sickle-shaped opercles, right side in lateral (left) and medial (right) views of A.Hemiancistrus medians, ANSP 187122, B.Pseudancistrus barbatus, ROM 86176, C.Colossimystax pectegenitor, AUM 42130, D.Stellantiasiderea,AUM 54310, E.Lithoxancistrus coquenani, AMNH 91025, F.Lithoxancistrus yekuana, AUM 39473. Scale bars = 1 cm.

Comparative material examined.Hemiancistrus medians, ANSP 187122, 155.1 mm SL, Lawa River, Marowijne drainage, Suriname. Lithoxancistrus coquenani, AMNH 91025, size not recorded, Orinoco drainage, Venezuela. Lithoxancistrus yekuana, AUM 39473, 42.7 mm SL, Orinoco drainage, Venezuela. Pseudancistrus barbatus, ROM86176, 121.7 mm SL, Essequibo drainage, Guyana. Pseudancistrus megacephalus,BMNH 1978.9.12.3, holotype, size not recorded. Pseudancistrus nigrescens, AUM 35742, 137.2 mm SL, Essequibo drainage, Guyana.

ACKNOWLEDGEMENTS

This project was partially funded by Planetary Biodiversity Inventory: All Catfish Species (Siluriformes), United States National Science Foundation Grant DEB–0315963 and NSF DEB–0707751 to JWA, NSF OISE–1064578 (International Research Fellowship), an NSERC Discovery Grant, and a National Geographic Committee for Research and Exploration grant #8721–09 to NKL, and various fieldwork grants from the Coypu Foundation to JWA and NKL. We thank Donald Taphorn and Oscar León (in memoriam) at the Museo de Ciencias Naturales in Guanare (MCNG) for aid in arranging field work in Venezuela and all those that helped in collecting specimens, particularly Mark Sabaj (ANSP) and David Werneke (AUM). We would like to thank them as well as Scott Schaefer, Tom Vigliotta, and Rad Arrindell (AMNH), James Maclaine, Oliver Crimmen, and Rupert Collins (BMNH), Mary Ann Rodgers and Kevin Swagel (FMNH), Raphael Covain and Sonia Fisch-Muller (MHNG), Richard Vari (in memoriam), Dianne Pitassy, and Sandra Raredon (NMNH), Erling Holm, Mary Burridge, and Don Stacey (ROM) for loan of materials and access to collections. We thank Hernán Lopéz-Fernandéz (ROM, UMMZ) and Nathan Lovejoy (University of Toronto Scarborough) for aid in developing the molecular phylogeny referred to in this paper, Emmanuel Neuhaus for translating the abstract to Portuguese, Morgan Chase (AMNH) and Alexander Tinius (University of Toronto) for assisting with CT-scanning, and University of Toronto student researchers Eunice Huang, Alice Lo, Jolie Nguyen, Amina Sharif, Christine Tang, Chunnan Yue for assistance with segmenting CT-data.

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ADDITIONAL NOTES

• Ethical Statement
  Not applicable.
• HOW TO CITE THIS ARTICLE
  Armbruster JW, Lujan NK. New tribe-level classification of Hypostominae (Loricariidae) based on optimization of morphological states on DNA-based relationships, with descriptions of three new tribes and two new genera. Neotrop Ichthyol. 2024; 22(4):e240108. https://doi.org/10.1590/1982-0224-2024-0108

• Edited-by
  George Mattox

Publication Dates

• Publication in this collection
  10 Jan 2025
• Date of issue
  2024

History

• Received
  11 July 2024
• Accepted
  31 Oct 2024