Melanorivulus ignescens, Costa, Wilson J. E. M., 2017

Costa, Wilson J. E. M., 2017, Three new species of the killifish genus Melanorivulus from the central Brazilian Cerrado savanna (Cyprinodontiformes, Aplocheilidae), ZooKeys 645, pp. 51-70 : 52-55

Melanorivulus ignescens sp. n. Figs 1, 2, Table 1

Holotype.

UFRJ 6875, male, 27.7 mm SL; Brazil: Mato Grosso state: Guiratinga municipality: stream tributary to Rio Bandeira, Rio das Garças drainage, Rio Araguaia drainage, 16°21'54"S, 53°47'58"W, altitude approximately 520 m asl, road MT-270, approximately 3 km southwest of the village of Guiratinga; W. J. E. M. Costa et al., 11 August 2016.

Paratypes.

UFRJ 6876, 13 males, 15.8-25.5 mm SL, 18 females, 17.7-23.4 mm SL; UFRJ 6877, 2 males, 24.0-25.1 mm SL, 2 females, 22.4-23.4 mm SL (C&S); CICCAA00277, 1 male, 20.6 mm SL, 1 female, 18.6 mm SL; collected with holotype.

Diagnosis.

Melanorivulus ignescens is distinguished from all other species of the Melanorivulus dapazi group by having the anal fin, in adult males, bright reddish orange (vs. yellow in Melanorivulus dapazi , Melanorivulus flavipinnis , and Melanorivulus regularis ). Also distinguished from all other congeners of the Melanorivulus dapazi group by the following combination of character states: 5-6 pelvic-fin rays (vs. 7 in Melanorivulus dapazi and Melanorivulus regularis ); 29-31 scales in longitudinal series (vs. 35-37 in Melanorivulus regularis ); female caudal spot inconspicuous in live fish (vs. conspicuous in Melanorivulus dapazi and Melanorivulus regularis ); caudal fin, in males, without red bars and distinctive orange margin (vs. with red bars in Melanorivulus regularis and Melanorivulus flavipinnis , with broad bright orange band along the whole margin in Melanorivulus dapazi ); in females, ventral surface of the head with dark grey spots, often forming short stripe on the chin (vs. without dark grey spots in Melanorivulus dapazi ); caudal-fin short, its length 26.8-33.1% SL (vs. long, its length 34.1-38.7% SL in Melanorivulus flavipinnis ). Also distinguished from all other species of the Melanorivulus dapazi group by having a constriction on the metapterygoid (vs. constriction absent).

Description.

Morphometric data appear in Table 1. Body slender, sub-cylindrical anteriorly, slightly deeper than wide, compressed posteriorly. Greatest body depth at vertical just in front of pelvic-fin base. Dorsal and ventral profiles of trunk almost straight to 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. Jaws short, snout weakly pointed in lateral view.

Dorsal and anal fins short, extremity slightly pointed in males, rounded in females. Caudal fin oval, slightly longer than deep. Pectoral fin rounded, posterior margin reaching vertical at 80-90% of length between pectoral-fin and pelvic-fin bases. Pelvic fin small, tip reaching between urogenital papilla and base of 1st anal-fin ray in males, reaching between anus and urogenital papilla in females; pelvic-fin bases medially in close proximity. Dorsal-fin origin on vertical through base of 8th anal-fin ray. Dorsal-fin rays 9-11; anal-fin rays 13-15; caudal-fin rays 30-31; pectoral-fin rays 13; pelvic-fin rays 5-6. No contact organs on fins.

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 F-patterned, rarely E-scale anteriorly overlapping F-scale; E-scales not overlapping medially; scales arranged in regular circular pattern around A-scale without exposed margins. Longitudinal series of scales 29-31; 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 + 11 + 1, preorbital 2, otic 1, post-otic 1-2, supratemporal 1, median opercular 1, ventral opercular 1, pre-opercular 2 + 4, mandibular 2-3 + 1, lateral mandibular 1, paramandibular 1.

Jaw teeth numerous, conical, irregularly arranged, outer teeth larger and slightly curved, inner teeth straight. Ventral process angulo-articular short, pointed. Ventral process of palatine short, slightly contacting quadrate. Mesopterygoid slender, posterior tip not reaching metapterygoid. Metapterygoid sub-rectangular, with constriction on middle portion. Dorsal portion of preopercle short and pointed, channel rudimentary. Basihyal sub-triangular, greatest width 50% of length; basihyal cartilage nearly 15% of total basihyal length. Six branchiostegal rays. Second pharyngobranchial teeth absent. Interarcual cartilage rudimentary. Fourth ceratobranchial teeth present, continuously arranged. Gill-rakers on first branchial arch 1 + 8. Vomerine teeth 2-4. Dermosphenotic present. Ventral process of posttemporal absent. 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 30-31.

Colouration.

Males. Flank metallic green-blue to metallic light green, sometimes purple-blue above anal fin; oblique narrow orangish red bars irregularly arranged, often forming chevron-like marks anteriorly directed; horizontal rows of reddish orange dots on anteroventral part of flank, between bases of pectoral and pelvic fins; pale dark grey blotches on postorbital region mainly visible when fish is exposed to strong light. Dorsum light brown with black dots, venter white. Dorsal portion of head side light brown, ventral portion white; pale golden iridescence on opercular region. Jaws dark grey. Iris pale yellow, sometimes with dark brown bar on anterior and posterior portions. Dorsal fin light yellow with two or three oblique dark red bars on posterior portion of fin. Anal fin reddish orange in adult exemplars to yellowish orange in juveniles, basal portion bluish white, distal region becoming gradually dark red-brown, distal margin with high concentration of melanophores. Caudal fin light yellow, often with faint orange spots on middle portion; sometimes pale bluish posterior margin. Pectoral fin hyaline. Pelvic fin orange.

Females. Side of trunk and head similar to males, but with paler colours. Ventral surface of head white, with dark grey spots often forming short stripe on chin. Dorsal fin pale yellow, with transverse series of grey spots; broad dark grey to black band on distal margin. Anal fin green-yellow, basal portion light blue with small red spots. Caudal fin pale yellow, with three or four dark grey bars, often interrupted; small black spot, smaller than pupil, on dorso-basal portion of fin overlapping anterior-most bar, more conspicuous in preserved specimens; broad dark grey to black band on whole fin margin.

Distribution.

Known only from the type locality area, a small stream tributary to the Rio Bandeira, Rio das Garças drainage, upper Rio Araguaia basin, central Brazil, altitude approximately 520 m asl (Fig. 3).

Etymology.

From the Latin, ignescens (becoming inflamed), an allusion to the orange anal fin in males.