A new long-finned Corydoras Lacépède , 1803 ( Siluriformes : Callichthyidae ) from the lower rio Paraná basin , Brazil

A new species of Corydoras is described from the lower rio Paraná basin, just downstream from Itaipu Dam, Brazil, close to Paraguay boundary. The new species can be distinguished from most of its congeners by the infraorbital 2 with a posterior laminar expansion conspicuously reduced, first and second dorsal-fin branched rays conspicuously elongated in males, mesethmoid entirely covered by skin, and by the presence of four to six irregular black or brownish blotches on the midline of the flank. The probable occurrence of the new species in the floodplain of the upper portion of the rio Paraná drainage is discussed.


Introduction
Callichthyidae is composed of catfishes having the flanks covered by two longitudinal series of dermal plates and currently comprises about 200 species (Reis, 2003;Eschmeyer, 2013).
Corydoras Lacépède harbors about 170 species, being the most species-rich genus of Siluriformes (Eschmeyer, 2013).Gosline (1940) performed the first comprehensive study including Corydoras species in his revision of the Callichthyidae.Thirty years later, Nijssen (1970) carried out a review of the Corydoras species from Suriname and additionally allocated them, with exception of four species, in nine groups based mainly in color pattern and some morphometric features.Subsequently, Nijssen & Isbrücker (1980) revised Corydoras, allocating the hitherto 94 known species in five groups.Phylogenetic studies that included species of Corydoras were also advanced, primarily by Britto (2003) and more recently by Alexandrou et al. (2011).
The rio Paraná is the second longest river in South America, being primarily separated in two ichthyofaunistic provinces, the upper portion of rio Paraná drainage and the Parano-Platense drainage, previously separated by the "cachoeira de Sete Quedas" (Bonetto, 1986).Currently, after submersion of the "cachoeira de Sete Quedas", the barrier between these two provinces was replaced by the Itaipu dam.The aim of this paper is to describe and formally name such species.

Material and Methods
Measurements were obtained using digital calipers to the nearest tenth of millimeter.Morphometric and meristic data were taken following Reis (1997), except for the exclusion of the length of the anal-fin spine that is absent in all Corydoradinae.The length of the pectoral-fin spine was included in the morphometric analysis and was taken from its base to its distal tip.Morphometrics are reported as percents of standard length (SL) and head length (HL).Homology of barbels follows Britto & Lima (2003).Some specimens were cleared and stained (c&s) according to the protocol of Taylor & Van Dyke (1985).Osteologic terminology was based on Reis (1998), except for the use of the terms parieto-supraoccipital instead of supraoccipital (Arratia & Gayet, 1995) and compound pterotic instead of pterotic-supracleithrum (Aquino & Schaefer, 2002).
Counts of vertebrae followed Britto et al. (2009).In the description, numbers between parenthesis represent the total number of specimens with those counts.Numbers followed by an asterisk refer to the counts of the holotype.Comparative data of Corydoras diphyes were obtained from Axenrot & Kullander (2003) Description.Morphometric data in Table 1.Head compressed with slightly convex dorsal profile; triangular in dorsal view.Snout slightly pointed.Head profile convex from snout to tip of posterior process of parieto-supraoccipital.Profile slightly convex along dorsal-fin base.Body profile between dorsal fin and adipose-fin spine slightly concave; concave from that point to caudal-fin base.Ventral profile of body nearly straight from isthmus to pectoral girdle; slightly convex from that point to pelvic girdle.Profile nearly straight from pelvic girdle to base of first anal-fin ray; concave from that point to 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 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 close to anterodorsal margin of orbit, separated from it by distance equal to diameter of naris.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 longer 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.Mesethmoid short, totally covered by thin layer of skin.Nasal elongate and slender, smoothly curved laterally, inner margin laminar; mesial border contacting frontal and mesethmoid; with two nasal pores.Frontal elongated, narrow, width less than half entire length; anterior projection short, size smaller than nasal length; epiphysial branch of supraorbital canal short, pore opening mesially on frontal.Frontal fontanel large, oval; posterior tip extension entering anterior margin of parieto-supraoccipital.Parieto-supraoccipital wide, posterior process long and contacting nuchal plate.Two laminar infraorbitals with minute odontodes; infraorbital 1 moderately developed, relatively slender; anterior portion with moderate expansion (Fig. 2a); infraorbital 2 small, conspicuously slender, with posterior laminar expansion very reduced (Fig. 2a), almost imperceptible in some specimens; posteroventral margin contacting supra-preopercle, dorsal tip contacting sphenotic.Interopercle covered by thin layer of skin, somewhat triangular, with anterior projection well developed.Preopercle slender, elongated, with minute odontodes sparse on external surface.Opercle elongated in shape, width nearly equal to, or smaller than half of its length; free margin smooth, without serrations and covered with small odontodes.Anteroventral portion of cleithrum exposed; posterolateral portion of scapulocoracoid exposed; minute odontodes sparse on exposed areas.Vertebral count 23(3); ribs 6(3), first pair conspicuously larger.
Dorsal fin roughly triangular, located just posterior to second dorsolateral body plate.Dorsal-fin rays II,8(20), posterior margin of dorsal-fin spine with 14 to 25 serrations, disposed along entire length of spine; proximal portion of dorsal spine without serrations in some specimens.Nuchal plate exposed with minute odontodes; spinelet short; dorsalfin spine very long, adpressed distal tip almost reaching or reaching to adipose-fin origin, its posterior margin with small Middle portion of caudal-fin base with small black dot.Caudal fin with three or four transverse black bars.

Sexual dimorphism.
Corydoras gryphus presents a sexual dimorphism very similar to that described for C. tukano and C. longipinnis, with the first and second branched dorsal-fin rays conspicuously elongated in males, almost reaching caudal-fin origin in some specimens.The first branched ray of the pectoral fin is elongated in males.The dorsal-and pectoral-fin spines are well-developed in both sexes but are slightly larger in adult males.Dorsal-and pectoral-fin spines have segmented expansions, similar to those exhibited by Aspidoras Ihering and Scleromystax Günther.Infraorbital 1 has well-developed odontodes in males.
Etymology.From the Latin, the specific name gryphus means griffon, mythical creature with a lion body and a head and wings of a hawk or eagle, in allusion to the conspicuous elongation of pectoral-fin spine and its first branched ray, like a wing in male specimens.A noun in apposition.
posterior portion of lateral ethmoid and above junction of frontal and lateral ethmoid; posterior and ventral margins of nasal capsule with platelets.Lateral portion of snout with platelets in some specimens (Fig. 2a).Ventral surface of body with few irregular platelets; platelets absent in some specimens.contrary to C. longipinnis and C. tukano females, which present dorsal spine not surpassing the origin of the last branched ray of dorsal fin.Despite elongation in dorsal-fin elements in other Corydoras species, no evidence correlates it with sexual dimorphism, as mentioned by Britto & Lima (2003: 89).Accordingly, the condition found in C. gryphus, C. longipinnis, and C. tukano is treated herein as distinct from that observed in the remaining species of Corydoras.
A revisionary study about Corydoras paleatus species complex conducted by the first author (Tencatt, 2013) indicates that Corydoras paleatus presents no sexually-dimorphic characters as reported to C. gryphus, C. longipinnis and C. tukano.Thus, long dorsal-finned specimens assigned as Corydoras paleatus are in fact misidentifications.
Among Corydoras species from the rio Paraná basin, Corydoras diphyes and C. flaveolus are the species that exhibit the most similar color pattern to Corydoras gryphus.However, the new species can be distinguished from both species by lacking dark spots on the head (vs.spots present on the dorsal portion of head and snout) and by having irregular and variable-in-size black blotches on midline of flank (vs.rounded blotches with similar size).Corydoras gryphus also presents pectoral and anal fins with black bars, whereas these fins are hyaline in C. diphyes.The new species also differs from C. diphyes by having the posterior margin of pectoral-fin spine with serrations along its entire length (vs.serrations only on distal half of the spine), a larger head (39.9-48.6% vs. 29.2-33.8% of SL), a shorter snout (29.3-36.6% vs. 48.5-56.0% of HL), conspicuous sexual dimorphism (vs.indistinct sexually dimorphic features), and by a higher number of vertebrae (22 excluding the Weberian complex, which are not reported in Axenrot & Kullander (2003), vs. 18 or 19).
The rio Paraná is the second longest river of South America, being the main tributary to the Río de La Plata (Agostinho & Júlio-Júnior, 1999).The continuous damming processes have caused many changes in its main channel (Graça & Pavanelli, 2007).The previous natural barrier between the two different ichthyofaunistic provinces of the rio Paraná basin is currently the Itaipu dam (Bonetto, 1986;Agostinho & Júlio-Júnior, 1999).However, after the conclusion of the "Canal da Piracema" at the end of 2002, the segregation of the ichthyofauna between lower and upper rio Paraná basins are not more effective, allowing circulation of some species through the different regions of the basin (Makrakis et al., 2007).Specimens of the new species were collected in the rio Paraná basin, just downstream from the Itaipu dam.Despite it had never been recorded in the floodplain of the upper rio Paraná hitherto, its occurrence is presumable there, mostly due to the Canal da Piracema.
Comparative Material.All lots of the comparative material available in Britto (2003) were analyzed.In addition, the following Remarks.Fuller & Evers (2011: 64-65) mentioned the presence of an undescribed species from the Misiones Province, Argentina (Fig. 5).The presence of irregular and slightly vertically elongated small black blotches along midline of the flank is shared between the new species and Corydoras sp.'Misiones' (see Figs. 1, 5).On the other hand, Corydoras sp.'Misiones' present irregular and striated black spots on the snout and dorsal portion of the head, which are absent in C. gryphus.However, Corydoras sp.'Misiones' present the same unusual sexual dimorphism of C. gryphus, C. longipinnis and C. tukano.Additionally, through the analysis of high-definition photographs, it was possible to observe that Corydoras sp.'Misiones' also presents a reduced laminar expansion of infraorbital 2 and relatively slender infraorbital 1, similar to C. gryphus condition.Furthermore, the type locality of C. gryphus is relatively near to the territory of Misiones Province.Despite the similarity between the new species and Corydoras sp.'Misiones', the precise confirmation that they are the same species can only be made through the analysis of preserved specimens of Corydoras sp.'Misiones'.

Discussion
The conspicuous slender infraorbital 2 with a very reduced posterior laminar expansion was not observed in any examined specimens from other species of Corydoras.Corydoras gryphus has this bone generally almost reduced to a canal whereas the remaining species have a relatively thicker (Fig. 2b) or very thick (see Tencatt et al., 2013: fig. 2c) infraorbital 2 bone due to the more developed posterior laminar expansions.Other interesting feature observed in the new species is the absence of the process in the pharyngobranchial 3, which is rounded or triangular in other species.However, the examined material of Corydoras gryphus is old and the c&s material is somewhat damaged which hampered the osteological analysis.Despite that, in all the examined material the process in pharyngobranchial 3 is absent, which suggests that this species, in fact, lacks this feature.
Color in alcohol.Ground color of body brownish yellow, with top of head dark brown.Head without spots.Region of nasal bone dark.Opercle with pale border; anterior portion dark brown.Upper portion of dorsolateral plates dark blotched.Dorsal series of four dark brown blotches, first on anterior portion of dorsal-fin base, second on posterior portion of dorsal-fin base, third on adipose-fin base and fourth on caudal-fin base.Midline of flank with four to six irregular black blotches, different in size from each other, generally elongated transversally.Inferior portion of ventrolateral body plates generally dark spotted posteriorly to pelvic fin.Dorsal and pectoral fins scarcely dark mottled.Pelvic fin hyaline.Adipose fin generally with hyaline membrane and with darkened area on distal portion of membrane in some specimens.Middle portion of anal fin with black blotch.
Calviño & Alonso and C. undulatus Regan, have been reported in the rio Paraná basin.Recent examination of specimens from the rio Paraná basin collected near the Itaipu dam revealed the presence of an undescribed species.
C. longipinnis by having the mesethmoid not visible, entirely covered by a thick layer of skin (vs.visible, posterior portion of mesethmoid covered by a very thin epidermal layer).See additional diagnostic features in the discussion.