Corydoras brittoi, Tencatt & Ohara, 2016

Tencatt, Luiz Fernando Caserta & Ohara, Willian Massaharu, 2016, Two new species of Corydoras Lacépède, 1803 (Siluriformes: Callichthyidae) from the rio Madeira basin, Brazil, Neotropical Ichthyology (Neotrop. Ichthyol.) 14 (1), No. e 150063, pp. 1-16 : 2-7

Corydoras brittoi , new species

urn:lsid:zoobank.org:act:3F9B3430-8D4C-4180-9B82-1E70648E7BD1

( Figs. 1-2a,b , 3a,c , 4 , Table 1)

Holotype. MNRJ 43316 , 38.1 mm SL, Brazil, Mato Grosso State, Colniza Municipality, Guariba District, tributary to the rio Guariba , rio Aripuanã drainage, rio Madeira basin, 09°06’47.4”S 60°25’14.1”W, 15 Jul 2013, W. M. Ohara, D. B. Hungria & B. Barros.

Paratypes. All from Brazil, Mato Grosso State, Colniza Municipality, Guariba District , rio Aripuanã drainage, rio Madeira basin . NUP 17311, 2 , 32.4-35.2 mm SL, rio Aripuanã , 09°21’00”S 59°19’33”W, 16 Jul 2013, W. M. Ohara, D. B. Hungria & B. Barros ; ZUFMS-PIS 4063 , 1 , 38.1 mm SL, Igarapé Pica-Pau, a tributary to the rio Juma , 09°22’27.2”S 60°02’59.9”W, 16 Jul 2013, W. M. Ohara, D. B. Hungria & B. Barros . INPA 48032 , 4 , 34.7-36.7 mm SL ; MCP 48747, 3 , 34.5 -39.0 mm SL ; MNRJ 43573 , 4 , 32.7-36.8 mm SL ; MZUSP 117334 , 5 , 35.4-37.5 mm SL ; NUP 17312, 4 , 34.8-37.4 mm SL ; NUP 17313, 2 c&s, 31.4-34.1 mm SL; same data as the holotype .

Diagnosis. Corydoras brittoi can be distinguished from all of its congeners, with exception of the species from ‘lineage 8’ sensu Alexandrou et al. (2011), by the presence of posterior margin of dorsal-fin spine with laminar serrations directed towards the origin of the spine (vs. serrations, when present, conical; directed towards dorsal-fin spine tip in the members of the remaining lineages). Corydoras brittoi can be distinguished from other members of ‘lineage 8’, with exception of C. bifasciatus Nijssen, 1972 , C. pinheiroi Dinkelmeyer, 1995 and C. pulcher , by the presence of two longitudinal black stripes on flanks (vs. presence of a single arched black stripe on dorsal portion of flank in C. arcuatus ; stripe, when well defined, located on midline of flank in C. gomezi , C. incolicana Burgess, 1993 , C. leopardus , C. orphnopterus , C. robineae Burgess, 1983 and C. robustus ; three to four slender longitudinal black stripes on flanks in C. ornatus ; presence of three to four longitudinal rows of black spots on flanks, which may be coalescent and form stripes in some specimens of C. haraldschultzi , C. isbrueckeri , C. noelkempffi and C. spectabilis ; absence of stripes on flanks in remaining species). Corydoras brittoi can be distinguished from C. bifasciatus and C. pulcher by presenting anterior portion of dorsal fin with sparse black chromatophores, not forming any conspicuous pattern (vs. conspicuously blackened in C. bifasciatus ; hyaline with conspicuous whitish yellow pigmentation in C. pulcher ); from C. pinheiroi by the absence of a conspicuous black marbled coloration pattern on head (vs. presence). Additionally, Corydoras brittoi can also be distinguished from C. bifasciatus by the presence of black spots on caudal fin, some spots arranged, forming transversal bars (vs. spots absent, covered by brown chromatophores); from C. pulcher by the presence of brownish dorsal-fin spine (vs. conspicuously whitish yellow).

Description. Morphometric data presented in Table 1. Head compressed with acutely convex dorsal profile; triangular in dorsal view. Snout pointed and straight. Head profile nearly straight from tip of snout to anterior nare; ascending nearly straight from this point to tip of posterior process of parietosupraoccipital. 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 base of first anal-fin ray; concave from this point to caudal-fin base. Body acutely 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 relatively large, almost 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.

Mesethmoid long; anterior tip well developed, larger than 50% of bone length (see Britto, 2003: 123, character 1, state 0; fig. 1A); posterior portion conspicuously narrow and entirely covered by a thick layer of skin. Nasal slender, curved laterally, with very reduced laminar expansion on its inner margin; mesial border contacting only frontal. Frontal elongated, narrow, with width slightly smaller than half of entire length; anterior projection short, size smaller than nasal length. Frontal fontanel large, oblong; posterior tip extension slightly entering anterior margin of parietosupraoccipital. Parieto-supraoccipital wide, posterior process long and contacting nuchal plate; region of contact between posterior process and nuchal plate covered by thick layer of skin.

Two laminar infraorbitals with minute odontodes; infraorbital 1 large, ventral laminar expansion poorly 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. 2b ). Posterodorsal ridge of hyomandibula close to its articulation with opercle oblong; exposed, conspicuously slender; dorsal ridge of hyomandibula between compound pterotic and opercle covered by thick layer of skin; exposed areas bearing small odontodes. Interopercle covered by thin layer of skin, somewhat triangular, anterior projection well-developed. Preopercle slender, elongated, minute odontodes sparse on external surface. Opercle elongated dorso-ventrally, width smaller than half of its length; free margin 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 22 (2); ribs 7 (2), first pair conspicuously large; complex vertebra slender in shape. Neural and haemal spines with pointed 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 a very reduced process on anterior margin of mesial portion; ceratobranchial 3 notched on postero-lateral margin; ceratobranchial 5 toothed on postero-dorsal surface, 34 to 36 (2) teeth aligned in one row. Four epibranchials with similar size; epibranchial 2 slightly larger than others, with small pointed process on laminar expansion of posterior margin; epibranchial 3 with somewhat quadrangular uncinate process on laminar expansion of posterior margin. Two wide pharyngobranchials (3 and 4), pharyngobranchial 3 with a rippled laminar expansion on posterior margin. Upper tooth plate oval; 34 to 40 (2) 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; slightly directed toward frontal fontanel region. 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 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.

Dorsal fin triangular, located just posterior to second dorsolateral body plate. Dorsal-fin rays II,8, posterior margin of dorsal-fin spine 11 to 14 moderately-developed serrations directed towards dorsal-fin spine origin; serrations absent proximally ( Fig. 3a ). Nuchal plate moderately developed; exposed, with minute odontodes; spinelet short; spine moderately developed, adpressed distal tip reaching to or slightly surpassing origin of last dorsal-fin branched ray; anterior margin with small odontodes. Pectoral fin triangular, its origin just posterior to gill opening. Pectoralfin rays I,8 (17), I,9* (3); posterior margin of pectoral-fin spine with 17 to 19 moderately-developed laminar serrations along its entire length; serrations directed towards pectoralfin spine origin ( Fig. 3c ). Pelvic fin oblong, located just below first ventrolateral body plate, and at vertical through first branched dorsal-fin ray. Pelvic-fin rays i,5. Adipose fin roughly triangular, separated from base of last dorsalfin ray by generally six dorsolateral body plates. Anal fin triangular, located just posterior to 13 th ventrolateral body plates, and at vertical through anterior margin of adiposefin spine. Anal-fin rays ii,6. Caudal-fin rays i,12,i, generally five dorsal and ventral procurrent rays; bilobed; dorsal lobe generally slightly larger than ventral lobe.

Three laterosensory canals on trunk; first ossicle tubular, second ossicle laminar, third lateral-line canal encased in third dorsolateral body plate. Body plates with minute odontodes scattered over exposed area, a conspicuous line of odontodes confined on posterior margins; dorsolateral body plates 22 (4), 23* (14), 24 (2); ventrolateral body plates 20* (12), 21 (8); dorsolateral body plates along dorsal-fin base 6* (18), 7 (2); dorsolateral body plates between adipose and caudal fins 6 (7), 7* (12), 8 (1); preadipose platelets 2 (1), 3* (18), 4 (1); small platelets covering base of caudalfin rays; small platelets disposed dorsally and ventrally between junctions of lateral plates on posterior portion of caudal peduncle. Anterior margin of orbit, above lateral ethmoid, dorsal surface of snout, nasal capsule region, and upper lip covered by platelets bearing odontodes. Ventral surface of trunk covered by sparse irregular platelets bearing odontodes.

Color in alcohol. Overall color of body in Fig. 1 . Ground color of body pale yellow, with top of head and snout dark brown; interorbital region with more intense brown pigmentation; nuchal plate and border of process of parietosupraoccipital contacting first dorsolateral body plate light yellow. Medial portion of opercle and cleithrum, posterior portion of compound pterotic, preopercle, infraorbitals 1 and 2, upper lip, maxillary barbel and anterior portion of outer mental barbel covered by brownish chromatophores. First, second and third dorsolateral body plates almost entirely blackened. Dorsal portion of body irregularly black pigmented, forming diffuse longitudinal black stripe; black stripe larger on dorsal-fin base region becoming narrow towards caudal peduncle. Body with two conspicuous longitudinal black stripes. Midventral half of dorsolateral body plates blackened, forming broad longitudinal stripe along flank. Medial portion of ventrolateral body plates anterior to anal-fin last branched ray region blackened, forming slender longitudinal black stripe along flank. Dorsal fin covered by sparse black chromatophores; chromatophores slightly more concentrated on region of first and second dorsal-fin rays, including membranes; chromatophores generally absent close to dorsal-fin base; dorsal-fin spine brownish. Pectoral-fin rays with sparse black chromatophores; pectoral-fin spine brownish. Pelvic fin hyaline. Adipose fin covered by black chromatophores on its medial portion; black pigmentation more intense, forming an irregular conspicuous elongated black blotch in some specimens; adipose-fin spine dorsal half blackened. Caudal-fin base blackened; caudal-fin lobes with black spots; some spots arranged in one to four transversal black bars.

Color in life. Very similar to preserved specimens but with ground color of body whitish yellow. Region of contact between process of parieto-supraoccipital and nuchal plate bright yellow. Body covered by greenish yellow iridescent coloration, more concentrated on lower half of opercle, infraorbitals, cleithrum and on region of two longitudinal lateral stripes ( Fig. 4 ).

Sexual dimorphism. Except for the presence of lanceolate genital papilla in males, which occurs in all Corydoradinae (see Nijssen & Isbrücker, 1980; Britto, 2003), no other sexually dimorphic feature was observed.

Distribution. The new species is known from the rio Aripuanã basin, Mato Grosso State ( Fig. 5 ).

Ecological notes. The type locality of Corydoras brittoi is located at 110 meters above sea level, and is a small clear water stream, with 2-3 m width and 0.5-2 m depth, with preserved riparian vegetation, swift water current, and bottom composed mainly of sand and dead leaves. Specimens of C. brittoi were observed at night during capture at shallow portions of the stream in small groups (5-15 individuals), and sometimes associated with a other new species described below.

Etymology. Corydoras brittoi is named in honor of Marcelo Ribeiro de Britto, a dear friend and mentor, for his extensive contributions to the taxonomy and systematics of the Corydoradinae . A genitive.

Conservation status. Corydoras brittoi is so far known only from the type-locality and its conservation status is uncertain based on the limited knowledge of its geographic distribution. However, considering that important threats to the species were not detected in the area, and that it occurs in a protected area (Reserva Extrativista Guariba Roosevelt), Corydoras brittoi would be classified as Least Concern (LC) according to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN Standards and Petitions Subcommittee, 2014).

Figures

Fig. 1. Corydoras brittoi, holotype, MNRJ 43316, 38.1 mm SL, Brazil, Mato Grosso State, Colniza Municipality, Guariba District, tributary to the rio Guariba, rio Aripuanã drainage, rio Madeira basin, 09°06’47.4”S 60°25’14.1”W. Dorsal (top), lateral (middle) and ventral (bottom) views. Photo by Celso Ikedo.

Fig. 2. Lateral view of the head of c&s specimens of Corydoras brittoi, NUP 17313, 34.1 mm SL, showing the poorlydeveloped ventral expansion of the infraorbital 1 (a) and infraorbital 2 in contact with compound pterotic (b), and of Corydoras pavanelliae, NUP 17315, 25.4 mm SL, showing the poorly-developed ventral expansion of the infraorbital 1 (c) and infraorbital 2 not in contact with compound pterotic (d). The dotted lines in (b) and (d) represent the suture between sphenotic and compound pterotic bones. Abbreviations: io1: infraorbital 1, io2: infraorbital 2, sph: sphenotic, cpt: compound pterotic. Scale bar = 1.0 mm.

Fig. 3. Dorsal- and pectoral-fin spines of (a, c) Corydoras brittoi, NUP 17313, 34.1 mm SL, showing serrations directed towards the origins of the spines on posterior margins of the (a) dorsal-fin spine (8.6 mm long) and of the (c) right pectoral-fin spine (8.9 mm long), and of (b, d) Corydoras pavanelliae, NUP 17315, 26.8 mm SL, showing serrations directed towards the tips of the spines on posterior margins of the (b) dorsal-fin spine (7.9 mm long) and of the (d) right spine (7.6 mm long).

Fig. 4. Specimen of Corydoras brittoi photographed in life, showing the iridescent greenish yellow coloration all over thebody.

Fig. 5. Map showing the type-locality (red circle) of Corydoras brittoi and Corydoras pavanelliae, a tributary to the rio Guariba, Mato Grosso. The blue triangle represents the Igarapé Pica-Pau, also a tributary to the rio Guariba, and the yellow triangle represents the rio Aripuanã, both representing additional records of C. brittoi.