A new Corydoras Lacépède, 1803 (Siluriformes: Callichthyidae) from the rio Araguaia basin, Brazil, with comments about Corydoras araguaiaensis Sands, 1990

A new species of Corydoras is described from the rio Araguaia basin, Goias, Brazil. The new species can be distinguished from its congeners by presenting the following features: infraorbital 1 with very large ventral laminar expansion; infraorbital 2 contacting compound pterotic; flanks densely covered by irregular black spots; and ventral surface of trunk densely covered by coalescent relatively well-developed platelets. It is also discussed the possibility that C. araguaiaensis comprehends a complex of species.

Currently, only three species of Corydoras are recorded from the rio Araguaia basin: C. araguaiaensis Sands, 1990, C. cochui Myers & Weitzman, 1954, and C. maculifer Nijssen & Isbrücker, 1971 (Eschmeyer, 2015).Alexandrou et al. (2011) studied the community structure of mimetic lineages of Corydoras propitiated by ecological and phylogenetic aspects, showing relations and patterns between Müllerian co-mimics of certain regions.In that work, C. araguaiaensis is proposed as member of a mimetic group along with C. maculifer and an undescribed species coded as C122 (see more details about the "C-number" system and its species in Fuller & Evers, 2005: 280).The most obvious way to recognize each mimetic morphotype is the snout morphology.There are at least three conspicuous types of snouts, the typical long snout pattern, present in the species of the lineage 1, as C. maculifer, the straight or intermediate long snout pattern, present in the species of the lineage 8, as C122, and the short snout pattern, present in the species of the lineages 4, 5, 6, 7, and 9, as C. araguaiaensis.
Generally, the mimetic pairs or groups are composed by one representative of each snout pattern (see Alexandrou et al., 2011: 3, fig.2).However, since the short snout pattern is present in conspicuously different lineages, it is possible that two or more short-snouted species may also present homoplastic color patterns, as the observed for Corydoras guapore Knaack, 1961, from the lineage 4, and C. caudimaculatus Rössel, 1961, from the lineage 9, both from the rio Guaporé basin (see Alexandrou et. al., 2011: suppl. fig. 2).After the analysis of some Corydoras specimens captured by Hans-Georg Evers during an expedition in Brazil, a new short-snouted species with similar color pattern to C. araguaiaensis was revealed, which is described herein.Additionally some comments about the taxonomic status of C. araguaiaensis were also provided.
Head compressed with convex dorsal profile; triangular in dorsal view.Snout short and rounded.Head profile convex from tip of snout to anterior nares; ascending nearly straight from this point to tip of posterior process of parieto-supraoccipital; region just posterior to eye slightly concave in some specimens.Profile slightly convex along dorsal-fin base.Postdorsal-fin body profile nearly straight to adipose-fin spine; concave from this point to caudal-fin base.Ventral profile of body slightly convex from isthmus to pelvic girdle.Profile nearly straight from pelvic girdle to base of first anal-fin ray; concave until caudal-fin base.
Body roughly elliptical in cross section at pectoral girdle, gradually becoming more compressed toward caudal fin.
Eye rounded, located dorso-laterally on head; orbit delimited dorsally by lateral ethmoid, frontal and sphenotic, ventrally by infraorbitals.Anterior and posterior nares close to each other, only separated by flap of skin.Anterior naris tubular.Posterior naris relatively distant to anterodorsal margin of orbit, separated from it by distance equal to twice of naris diameter.Mouth small, subterminal, width nearly equal to bony orbit diameter.Maxillary barbel moderate in size, not reaching anteroventral limit of gill opening.Outer mental barbel slightly larger than maxillary barbel.Inner mental barbel fleshy, with base close to its counterpart.Small rounded papillae covering entire surface of all barbels, upper and lower lips, and isthmus.Two laminar infraorbitals with minute odontodes; infraorbital 1 large, ventral laminar expansion well developed; anterior portion with well-developed expansion (Fig. 2a); infraorbital 2 small, slender; with posterior laminar expansion well developed; posteroventral margin contacting posterodorsal ridge of hyomandibula, dorsal tip contacting sphenotic and compound pterotic (Fig. 2c).Posterodorsal ridge of hyomandibula close to its articulation with opercle oblong; exposed, relatively thick; dorsal ridge of hyomandibula between compound pterotic and opercle exposed; exposed areas bearing small odontodes.Interopercle entirely or almost entirely covered by thick layer of skin, somewhat triangular, anterior projection well-developed.Preopercle relatively thick, elongated, minute odontodes sparse on external surface.Opercle conspicuously elongated dorso-ventrally, width smaller than half of its length; free margin smoothly convex, without serrations and covered by small odontodes.Anteroventral portion of cleithrum and posterolateral portion of scapulocoracoid exposed; minute odontodes sparse on exposed areas.Vertebral count 20 (2), 21 (1); ribs 6 (3), first pair conspicuously large; complex vertebra compact in shape.Neural and haemal spines with expanded in distal tips.
Four branchiostegal rays decreasing in size posteriorly.Hypobranchial 2 somewhat triangular, tip ossified and directed towards anterior portion, posterior margin cartilaginous; ossified portion well developed, about twice size of 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 postero-dorsal surface, 37 to 46 (3) 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 curved mesially uncinate process on laminar expansion of posterior margin.Two wide pharyngobranchials (3 and 4), pharyngobranchial 3 with irregular laminar expansion on posterior margin.Upper tooth plate oval; 34 to 43 (3) teeth aligned in two rows on postero-ventral surface.Lateral-line canal entering neurocranium through compound pterotic, splitting into two branches before entering sphenotic: pterotic branch with a single pore; preoperculomandibular branch conspicuously reduced, with a single pore opening close to postotic main canal.Sensory canal continuing through compound pterotic, entering sphenotic as temporal canal, which splits into two branches: one branch giving rise to infraorbital canal, other branch entering frontal through supraorbital canal, both with single pore.Supraorbital canal not branched, running through nasal bone.Epiphyseal pore opening at supraorbital main canal.Nasal canal with three openings, first on posterior edge, second on posterolateral portion and third on anterior edge.Infraorbital canal running through entire second infraorbital, extending to infraorbital 1 and opening into two or three pores.Preoperculomandibular branch giving rise to preoperculo-mandibular canal, which runs through entire preopercle with three openings, leading to pores 3, 4, and 5, respectively.
Sexual dimorphism.Presence of lanceolate genital papilla in males, which occurs in all Corydoradinae (see Nijssen & Isbrücker, 1980;Britto, 2003).The males of the new species present first and second branched dorsal-fin rays slightly larger than in females.Additionally, the males of Corydoras eversi present pointed oblong pelvic fin, while in females the pelvic fin is rounded.In Corydoras females, the rounded pelvic fin is generally used to make a ventral pouch to hold the eggs during spawning (H.-G.Evers pers.comm.).
Distribution.Corydoras eversi is known from its type locality, an unnamed stream tributary to the rio Araguaia (Fig. 6).
Ecological notes.The specimens examined herein were captured in a clear water stream, with sandy ground and fast flowing.After capture the specimens are light orange.This color remains in aquarium when the water conditions are adequate to its biological aspects.In the type locality of the new species no other congener were observed in syntopy (H.-G.Evers pers.comm.).

Etymology. Corydoras eversi is named in honor of
Hans-Georg Evers, a dear friend and great enthusiast in the fishkeeping hobby, especially in the breeding of Corydoras species.Hans collected the specimens of C. eversi that apparently originated all the stock present in the hobby until the present day and also the specimens used herein for the description.trip has been performed in the region since 1998.Therefore, the current situation of the type locality is unknown and, with the available data, it is not possible to determine if any of the aforementioned potential threats has directly affected the new species.Additionally, it is very possible that the new species may be further spread than the type locality region, potentially occurring in other creeks and streams of the region.Thus, it seems like the most appropriate conservation status according to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN Standards and Petitions Subcommittee, 2014), is Least Concern (LC).
Remarks.Corydoras eversi is known by exporters and in the fishkeeping hobby as Corydoras sp."Guaraná" due to the intense and shiny orange pigmentation displayed by live specimens, which is very similar to the Brazilian lemonade.Evers (1998) coded the new species as C65, according to the "C-number" system proposed by Evers (1993).

Discussion
The new species present a color pattern similar to C. albolineatus Knaack, 2004, C. apiaka Espíndola, Spencer, Rocha & Britto, 2014, C. araguaiaensis, C. haraldschultzi Knaack, 1962, C. maculifer, C. multimaculatus Steindachner, 1907, C. polystictus Regan, 1912, and C. xinguensis Nijssen, 1972.Corydoras eversi can be clearly diagnosed from C. haraldschultzi and C. maculifer by the presence of short mesethmoid (vs.long) and serrations on posterior margin of pectoral spine directed towards the tip of the spine (vs.directed towards pectoral-spine origin).From C. albolineatus, C. apiaka, C. araguaiaensis and C. polystictus, the new species can be distinguished by the presence of infraorbital 2 in contact with compound pterotic (Fig. 2c) (vs.not in contact (Fig. 2d)).The new species differs from C. multimaculatus and C. xinguensis by the presence of ventral laminar expansion of infraorbital 1 well developed (vs.moderately developed) and ventral surface of the trunk densely covered by coalescent relatively well developed platelets (vs.covered by sparse relatively small platelets).
Corydoras eversi presents osteological pattern similar to the species from clade IX sensu Britto (2003).The presence of a well-developed ventral laminar expansion in the infraorbital 1 corresponds to the state 3 of character 15 of Britto's (2003) phylogeny, a synapomorphy of the species located in clade IX.This clade is composed of species previously allocated in Brochis Cope, 1871, in addition to C. aeneus, C. eques, C. rabauti, and C. zygatus.Corydoras melanotaenia also appeared correlated with the aforementioned species in the phylogenetic hypothesis conducted by Alexandrou et al. (2011).As presented in the diagnosis, the species mentioned above can be promptly distinguished from C. eversi by their peculiar general color pattern, with uniform background color and dark dorsal region, clearly different from the densely spotted pattern of the new species.Additionally, C. coppenamensis, C. difluviatilis, C. garbei, and C. lymnades also present a welldeveloped ventral laminar expansion in the first infraorbital.The new species can be clearly distinguished from these species by the presence of ventral surface of trunk densely covered by relatively large coalescent platelets (vs.ventral surface of trunk naked; or covered by sparse and relatively small platelets).
The presence of relatively well-developed coalescent platelets in the ventral surface of the trunk of Corydoras eversi (Fig. 4) is an uncommon condition only displayed by few congeners, such as C. araguaiaensis, C. esperanzae, C. evelynae, C. fowleri Böhlke, 1950, C. julii Steindachner, 1906, C. leopardus, C. orphnopterus, C. schwartzi, and C. trilineatus Cope, 1872.The new species can be distinguished from C. evelynae, C. orphnopterus, and C. schwartzi by the absence of a concentration of a transversal black stripe ("mask") across the eye (vs.presence).Corydoras eversi differs from C. julii, C. leopardus, and C. trilineatus by the absence of a conspicuous longitudinal black midlateral stripe bordered dorsally and ventrally by an unpigmented area (vs.presence).From C. araguaiaensis, the new species differs by the presence of infraorbital 1 with ventral laminar expansion well developed (Fig. 2a) (vs.moderately developed (Fig. 2b)) and relatively large platelets bearing odontodes on snout (vs.plates generally absent; when present, plates are scarce and restrict to the anterior margin of orbit, above lateral ethmoid).From C. fowleri, it can be distinguished by having short and rounded snout (vs.long and conspicuously pointed).Finally, C. eversi can be distinguished from C. esperanzae by the presence of black spots on the body (vs.absence).
Despite the great general resemblance between Corydoras eversi and C. araguaiaensis, both species present clearly different morphology, mainly in osteological features, as mentioned above.However, even the similar color pattern presents some conspicuous differences.The spots are smaller and more numerous in the new species (Fig. 1) whereas C. araguaiaensis presents larger and less numerous spots (Fig. 7).The caudal-fin color pattern is diffuse in C. eversi, with faded spots (Fig. 1), forming diffuse conspicuously slender transversal black bars only in few specimens, contrary to C. araguaiaensis which presents conspicuous and thicker transversal black bars on caudal fin (Fig. 7).
Evers (1993) proposed a coding system for the Corydoradinae to avoid the creation of nomina nuda by using trade names.Some potentially new species from the rio Araguaia basin with similar color pattern to Corydoras araguaiaensis were coded in this system, including C. eversi.Additionally, a species from the rio Cristalino basin, Mato Grosso State, very similar to C. araguaiaensis but with larger spots and more intense black pigmentation on anterior portion of dorsal fin, was considered new and coded as C45 (Fig. 8).Initially, C45 appears to be easily distinguished from C. araguaiaensis by its color pattern, but after a deep analysis the general morphology proved to be very similar, with mixed morphotypes, making all the aforementioned potential diagnostic features present some degree of overlap.By this reason, a clear diagnosis between C. araguaiaensis and C45 was not possible and they were treated herein as a single taxon.However, since the original description of C. araguaiaensis lacks many important information, mainly skeletal, beyond the existence of two different morphotypes, the possibility that C. araguaiaensis comprehends a complex of species is reasonable.A complete revisionary study of C. araguaiaensis, including a molecular approach, is needed to elucidate its taxonomic status.

Fig. 4 .
Fig. 4. Ventral surface of the trunk of Corydoras eversi, paratype, NUP 17310, 44.4 mm SL, showing the relatively large coalescent platelets covering the area between pectoral and pelvic girdles.Scale bar = 1.0 mm.Color in alcohol.Overall color of body in Fig. 1.Ground color of body brownish yellow, with top of head and snout dark brown.Ventral margin of orbit, above infraorbital 1, blackened.Maxillary barbel and anterior portion of outer mental barbel covered by black chromatophores.Dorsal and lateral portion of body, with exception of small region of ventrolateral body plates surrounding pelvic fin, densely covered by irregular black spots; spots arranged longitudinally on flanks, forming irregular stripes.Ventral region of body close to pectoral-fin spine origin with black spots in some specimens.Ground color of fins grayish brown.All fins covered by irregular black spots; pectoral, pelvic, anal, and caudal fins with black spots diffuse or absent in some specimens.Caudal fin generally with scattered spots, not forming transversal black bars; with faded spots arranged in up to six transversal slender black bars in few specimens.

Fig. 6 .
Fig. 6.Map showing the type locality (red star) of Corydoras eversi, an unnamed stream tributary to the rio Araguaia, Goiás State.Conservation status.At the time of the capture of Corydoras eversi, the type locality presented high degree of deforestation and presence of nearby cattle farming.There was an encampment of the ʻMovimento dos Trabalhadores Rurais Sem Terra -(MST)ʼ just a few kilometers away from the collection site (Hans-Georg Evers pers.comm.).Despite the type locality presents, at least in the year of 1998, nearby human and cattle occupation and severe deforestation, in addition to the scarcity of the known material of C. eversi, apparently, no additional collecting

Fig. 8 .
Fig. 8. Uncatalogued aquarium specimen of Corydoras araguaiaensis attributed to C45, showing the general color pattern of the species in lateral view.Photo by Hans-Georg Evers.