Melanorivulus nigromarginatus, Costa, Wilson J. E. M., 2018

Costa, Wilson J. E. M., 2018, Three new species of the killifish genus Melanorivulus from the Rio Parana Basin, central Brazilian Cerrado (Cyprinodontiformes, Aplocheilidae), Zoosystematics and Evolution 94 (1), pp. 17-27 : 19-22

Melanorivulus nigromarginatus sp. n. Figs 4, 5, Table 2

Holotype

UFRJ 8434, male, 27.6 mm SL; Brazil: Goiás state: Itarumã municipality: Córrego Lajeado, Rio Corrente drainage, upper Rio Paraná Basin, road GO-178, 18°49 ’45” S, 51°22 ’55” W, altitude about 470 m asl; W. J. E. M. Costa et al., 20 Sep. 2011.

Paratypes

Brazil: Estado de Goiás: Município de Itarumã: all from the Corrente River drainage, upper Paraná River Basin. UFRJ 8436, 5 males, 23.4-24.7 mm SL, 8 females, 23.0-27.7 mm SL; CICCAA 00693, 5 males, 19.4-23.5 mm SL, 5 females, 20.4-24.0 mm SL; UFRJ 8435, 1 male, 23.3 mm SL, 5 females, 22.5-25.4 mm SL (C&S); collected with holotype. - UFRJ 8440, 11 males, 25.4-35.6 mm SL, 7 females, 24.7-30.8 mm SL; UFRJ 8442, 4 males, 27.6-32.9 mm SL, 2 females, 26.6-27.9 mm SL (C&S); Córrego Barreiro, road GO-178, 18°50 ’30” S, 51°23 ’27” W, altitude 498 m; W.J.E.M. Costa et al., 15 Jan. 2007. - UFRJ 8439, 2 males, 27.0-30.0 mm SL, 1 female, 25.1 mm SL; same locality as UFRJ 8440; W.J.E.M. Costa et al., 20 Sep. 2011.

Diagnosis

Melanorivulus nigromarginatus is similar to M. egens and M. linearis , and distinguished from all other species of the M. pictus group by the presence of a black distal marginal stripe on the anal fin in males (vs. absence). Melanorivulus nigromarginatus is distinguished from M. egens and M. linearis by having melanophores strongly concentrated on the post-orbital and humeral regions, forming a stripe (vs. weakly concentrated, not forming distinct marks); presence of red dots on the anteroventral portion of flank (vs. absence); presence of red bars on most portion of caudal fin in males (vs. bars absent in M. egens and bars restricted to the dorsal portion of the caudal fin in M. linearis ); and red chevron-shaped marks irregularly distributed on the flank (vs. regularly). In addition, although not useful to distinguish all specimens, M. nigromarginatus often have more scales in the longitudinal series than M. egens and M. linearis (31-33 vs. 29-31).

Description

Morphometric data appear in Table 2. Body relatively deep, sub-cylindrical anteriorly, deeper than wide, compressed posteriorly. Greatest body depth at vertical just anterior to pelvic-fin base. Dorsal and ventral profiles of trunk slightly convex in lateral view; dorsal and ventral profiles of caudal peduncle nearly straight. Head moderately wide, sub-triangular in lateral view, dorsal profile nearly straight, ventral profile convex. Snout blunt. Jaws short; teeth numerous, conical, irregularly arranged; outer teeth hypertrophied, inner teeth small and numerous. Vomerine teeth 2-5. Gill-rakers on first branchial arch 1 + 8.

Dorsal and anal fins short, tip slightly pointed in males, rounded in females. Caudal fin rounded, slightly longer than deep. Pectoral fin rounded, posterior margin reaching vertical just anterior to pelvic-fin insertion. Pelvic fin small, longer in males, tip reaching between urogenital papilla and base of 2nd anal-fin ray in male, reaching anus in females; pelvic-fin bases medially in close proximity. Dorsal-fin origin at vertical between base of 8th and 9th anal-fin rays. Dorsal-fin rays 10-11; anal-fin rays 13-15; caudal-fin rays 31-34; pectoral-fin rays 13; pelvic-fin rays 6-7. No contact organs on fins. Second proximal radial of dorsal fin between neural spines of 19th and 21st vertebrae; first proximal radial of anal fin between pleural ribs of 13th and 15th vertebrae; total vertebrae 30-32.

Scales small, cycloid. Body and head entirely scaled, except anterior ventral surface of head. Body squamation extending over anterior 25 % of caudal-fin base; no scales on dorsal and anal-fin bases. Frontal squamation E-patterned; E-scales not overlapping medially; scales arranged in regular circular pattern around A-scale without exposed margins. Longitudinal series of scales 30-33; transverse series of scales 9; scale rows around caudal peduncle 16. No contact organs on scales. Cephalic neuromasts: supraorbital 3 + 3, parietal 1, anterior rostral 1, posterior rostral 1, infraorbital 1 + 10-12 + 1, preorbital 2, otic 1, post-otic 1, supratemporal 1, median opercular 1, ventral opercular 1, pre-opercular 2 + 4, mandibular 3 + 1, lateral mandibular 1-2, paramandibular 1.

Colouration

Males. Flank metallic light green, with narrow oblique red bars between humeral region and posterior portion of caudal peduncle; bars irregularly arranged, forming chevron pattern directed anteriorly, usually fragmented, with angle on flank midline or above it; bars with minute vertical extensions on each scale margin; dorsal portion of flank with oblique rows of red dots; anteroventral portion of flank with rows of red dots. Dorsum light brown, venter white. Side of head light brown on dorsal portion, yellowish white on ventral portion to pale golden on opercle; broad dark grey to black postorbital stripe, continuous to humeral black blotch; lower jaw dark grey. Iris pale yellow, with dark brown bar on anterior and posterior portions. Dorsal fin light yellow, with four to six oblique faint red bars. Anal fin light yellow to orange, basal portion greenish white with five or six orangish red spots, distal margin black. Caudal fin light yellow, with six to eight narrow orangish red bars extending on entire caudal fin, except its ventral-most portion. Pectoral fin hyaline. Pelvic fin light yellow to orange narrow black margin.

Females. Similar to males, except flank base colour pale greenish blue; dorsal and caudal fin bars dark grey; caudal fin base colour pale orangish pink; absence of black pigmentation on post-orbital and humeral regions; and presence of black spot on dorsal portion of caudal-fin base and dark grey pigmentation concentrated on distal margins of dorsal and anal fins, anterior margin of pelvic fin and entire caudal-fin margin.

Colouration in alcohol.

Head and trunk pale brown, fins whitish hyaline; dark marks recorded for live specimens varying from dark brown to black.

Distribution and conservation

Known only from two close small streams in the middle section of the Corrente River drainage, upper Paraná River Basin (Fig. 3).

Etymology

The name nigromarginatus (black margin), from the Latin, is a reference to the presence of a black margin on the anal in males.