Corydoras eversi, Tencatt & Britto, 2016

Tencatt, Luiz Fernando Caserta & Britto, Marcelo Ribeiro de, 2016, A new Corydoras Lacépède, 1803 (Siluriformes: Callichthyidae) from the rio Araguaia basin, Brazil, with comments about Corydoras araguaiaensis Sands, 1990, Neotropical Ichthyology (e 150062) 14 (1), pp. 1-12 : 2-8

Corydoras eversi , new species ur n:lsid:zooban k.org:act: 541C78B5-98B6 - 4FBF-89A3- 6961C9EA74D2

Figs. 1 , 2a, c , 3-5

Corydoras cf. araguaiaensis ‘C65’.- Alexandrou et al., 2011: 22 (supplement).

Corydoras sp. C 65.-Fuller & Evers, 2005: 282 [checklist], 309 [illustration].

Corydoras sp. ‘Guarana’ [sic].-Fuller & Evers, 2005: 310 [illustration].

Holotype. MNRJ 43195 , 44.5 mm SL, Brazil, Goiás, Montes Claros de Goiás, unnamed stream tributary to the rio Araguaia , 15°53’10”S 51°41’34”W, 21 Mar 1998, H.-G. Evers & P. V. da Silva.

Paratypes. MZUSP 117333 , 6 , 23.4-35.8 mm SL; NUP 17309, 5, 24.8-42.9 mm SL; NUP 17310, 3 c&s, 42.5- 45.3 mm SL; ZUFMS-PIS 4062, 5 , 32.2-39.2 mm SL, same data as holotype .

Diagnosis. Corydoras eversi can be distinguished from its congeners, with exception of C. aeneus ( Gill, 1858) , C. britskii (Nijssen & Isbrücker, 1983) , C. difluviatilis Britto & Castro, 2002 , C. eques Steindachner, 1876 , C. garbei Ihering, 1911 , C. melanotaenia , C. multiradiatus , C. rabauti , C. splendens ( Castelnau, 1855) , and C. zygatus Eigenmann & Allen, 1942 , by the presence of infraorbital 1 with very large ventral laminar expansion (vs. poorly-, or moderately-developed ventral expansion); and infraorbital 2 contacting compound pterotic (vs. not contacting). The new species can be distinguished from C. aeneus , C. britskii , C. difluviatilis , C. eques , C. garbei , C. melanotaenia , C. multiradiatus , C. rabauti , C. splendens , and C. zygatus by presenting flanks densely covered by irregular black spots (vs. background color of flanks orange yellow with dorsolateral body plates entirely or almost entirely blackened in C. aeneus , C. britskii , C. melanotaenia , C. multiradiatus , C. rabauti , C. splendens , and C. zygatus ; background color of flanks orange yellow with flanks almost entirely blackned in C. eques ; midline of flank with a longitudinal series of large rounded blotches, remaining areas with black spots in C. difluviatilis and C. garbei ); and ventral surface of trunk densely covered by coalescent relatively well-developed platelets (vs. ventral surface of trunk naked; or covered by sparse and relatively small platelets).

Description. Morphometric data presented in Table 1. 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.

Mesethmoid short; anterior tip poorly developed, smaller than 50% of bone length (see Britto, 2003: 123, character 1, state 1; fig. 1B); posterior portion relatively narrow, partially exposed and bearing minute odontodes. Nasal slender, curved laterally, with inner margin laminar; mesial border contacting frontal and mesethmoid. Frontal elongated, narrow, with width slightly smaller than half of entire length; anterior projection short, size smaller than nasal length. Frontal fontanel large, oval; posterior tip extension slightly entering anterior margin of parieto-supraoccipital. 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 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.

Dorsal fin triangular, located just posterior to second dorsolateral body plate. Dorsal-fin rays II,7 (1), II,8* (19), posterior margin of dorsal-fin spine with five to 14 very reduced serrations directed towards tip of spine; serrations absent proximally. 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. Pectoral-fin rays I,7 (10), I,8* (10); posterior margin of pectoral spine with 23 to 32 small serrations along its entire length; serrations directed towards tip of spine ( Fig. 3 ). 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 dorsal-fin ray by generally seven dorsolateral body plates. Anal fin triangular, located just posterior to 12 th ventrolateral body plates, and at vertical through anterior margin of adipose-fin spine. Anal-fin rays ii,5 (6), ii,6* (13). Caudal-fin rays i,7,i (1), i,11,i* (1), i,12,i (18), generally four dorsal and ventral procurrent rays; bilobed, dorsal lobe generally slightly larger than ventral lobe.

Three or four laterosensory canals on trunk; first ossicle tubular, second ossicle laminar, third and fourth lateral-line canals, if present, encased in third and fourth dorsolateral body plates, respectively. Body plates with minute odontodes scattered over exposed area, a conspicuous line of odontodes confined on posterior margins; dorsolateral body plates 21 (2), 22 (9), 23* (9); ventrolateral body plates 18 (1), 19 (8), 20 (10), 21* (1); dorsolateral body plates along dorsal-fin base 5* (6), 6 (14); dorsolateral body plates between adipose- and caudal-fin6 (10), 7*(9),8 (1);preadipose platelets2(3),3 (16), 4* (1); small platelets covering base of caudal-fin rays; small platelets disposed dorsally and ventrally between junctions of lateral plates on posterior portion of caudal peduncle. Anterior margin of orbit, above lateral ethmoid, snout, region surrounding ventral margin of preopercle, and upper lip covered with relatively large platelets bearing odontodes ( Fig. 2a ). Ventral surface of trunk covered by coalescent relatively well-developed platelets ( Fig. 4 ); region between pelvic and anal fins with platelets in some specimens.

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.

Color in life. Very similar to preserved specimens but with ground color of body intense orange; body covered by greenish yellow iridescent coloration ( Fig. 5 ).

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.

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 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).

Figures

Fig. 1. Corydoras eversi, holotype, MNRJ 43195, 44.5 mm SL, Brazil, Goiás, Montes Claros de Goiás, unnamed stream tributary to the rio Araguaia, 15°53’10”S 51°41’34”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 (a, c) Corydoras eversi, paratype, NUP 17310, 42.5 mm SL, showing the well-developed ventral expansion of the infraorbital 1 and the platelets on the snout (a) and infraorbital 2 in contact with compound pterotic (c); and (b, d) Corydoras araguaiaensis, MZUSP 87155, 31.8 mm SL, showing the moderately-developed ventral expansion of the infraorbital 1 (b) and infraorbital 2 not in contact with compound pterotic (d). The dotted lines in (c) and (d) represent the suture between sphenotic and compound pterotic. Abbreviations: io1: infraorbital 1, io2: infraorbital 2, sph: sphenotic, cpt: compound pterotic. Scale bar = 1.0 mm.

Fig. 3. Right pectoral spine (11.4 mm long) of Corydoras eversi, paratype, NUP 17310, 45.3 mm SL, showing the serrations on posterior margin.

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.

Fig. 5. Aquarium specimen of Corydoras eversi, nearly 37.0 mm SL, showing its peculiar bright orange color pattern. Photo by Hans-Georg Evers.

Fig. 6.Map showing the type locality (red star) of Corydoras eversi, an unnamed stream tributary to the rio Araguaia, Goiás State.