Melanorivulus regularis, 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 : 60-62

Melanorivulus regularis sp. n. Fig. 6, Table 3

Holotype.

UFRJ 6878, male, 26.9 mm SL; Brazil: Mato Grosso state: Alto Graças municipality: Ribeirão da Sobra, upper Rio Itiquira drainage, Rio Paraguai basin, 16°54'41"S, 53°37'55"W, altitude approximately 750 m asl, road BR-364; W. J. E. M. Costa et al., 5 August 2016.

Paratypes.

UFRJ 6879, 4 males, 24.4-33.3 mm SL, 9 females, 22.3-33.8 mm SL; UFRJ 6880, 2 males, 25.3-31.2 mm SL, 2 females, 23.7-28.4 mm SL (C&S); CICCAA00278, 1 male, 24.7 mm SL, 1 female, 25.9 mm SL; collected with holotype.

Diagnosis.

Melanorivulus regularis is distinguished from all other species of the Melanorivulus dapazi group by the presence, in males, of five or six dark reddish brown, regularly shaped and never interconnected bars on the caudal fin (vs. seven or eight narrow red bars, irregularly shaped and sometimes interconnected in Melanorivulus flavipinnis ; four or fewer short rudimentary bars, sometimes absent, in Melanorivulus dapazi ; bars always absent in Melanorivulus ignescens ). Also distinguished from all other congeners of the Melanorivulus dapazi group by the following combination of character states: 7 pelvic-fin rays (vs. 5-6 in Melanorivulus flavipinnis and Melanorivulus ignescens ); 35-37 scales in longitudinal series (vs. 29-32 in Melanorivulus flavipinnis and Melanorivulus ignescens ); caudal fin, in females, pale (vs. yellow on the middle portion and reddish orange on marginal region in M flavipinnis ); female caudal spot conspicuous in live exemplars fish (vs. inconspicuous in Melanorivulus flavipinnis and Melanorivulus ignescens ); caudal fin, in males, without distinctive orange margin (vs. with broad bright orange band along the whole margin in Melanorivulus dapazi ); anal fin, in males, yellow (vs. reddish orange in Melanorivulus ignescens ); in females, ventral surface of head with dark grey spots, often forming short stripe on chin (vs. without dark grey spots in Melanorivulus dapazi ). Also distinguished from all other congeners of the Melanorivulus dapazi group by having 32 vertebrae (vs. 29-31)

Description.

Morphometric data appear in Table 3. 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. Jaw teeth numerous, conical, irregularly arranged, outer teeth larger and slightly curved, inner teeth straight.

Dorsal and anal fins short, tip slightly pointed in males, rounded in females. Caudal fin oval, slightly longer than deep. Pectoral fin rounded, posterior margin reaching vertical at around 80% 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 anus in females; pelvic-fin bases medially in close proximity. Dorsal-fin origin on vertical through base of 8th anal-fin ray. Dorsal-fin rays 10-11; anal-fin rays 14-15; caudal-fin rays 31-33; pectoral-fin rays 13-14; pelvic-fin rays 7. 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 35-37; 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 + 10-11 + 1, preorbital 1-2, otic 1, post-otic 1, 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 near 55% of length; basihyal cartilage the 20% 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 + 7-8. Vomerine teeth 2-5. 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 14th and 15th vertebrae. Total vertebrae 32.

Colouration.

Males. Flank light metallic blue; oblique narrow orange-red bars irregularly arranged, often forming chevron-like marks anteriorly directed; horizontal rows of reddish orange dots on antero-ventral part of flank, between bases of pectoral and pelvic fins; dark brown pigmentation concentrated on postorbital, overlapped by black dots on superficial layer of skin. Dorsum light yellowish-grey, venter white. Dor sal portion of head side light brown, ventral portion white; pale golden iridescence on opercular region. Jaws dark grey. Iris pale yellow to pale brown. Dorsal fin pale yellow with four or five narrow red bars on posterior portion of fin. Anal fin orangish-yellow, basal portion white, posterior portion pale blue with two or three faint red oblique bars; distal region becoming gradually dark red-brown, distal margin with high concentration of melanophores. Caudal fin pale blue to pale yellow, with five or six dark red-brown regularly shaped bars, ventral portion light yellow without bars, ventral margin orangish-brown. Pectoral fin yellowish-hyaline. Pelvic fin pale blue with brown anterior margin.

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 three or four bars on posterior region; broad dark grey to black band on distal margin. Anal fin pale yellow, basal portion light blue. Caudal fin pale yellow, with four or five dark grey bars; small black spot, slightly smaller than pupil, on dorso-basal portion of fin; broad dark grey to black band on whole fin margin.

Distribution.

Known only from the type locality, Ribeirão da Sobra, an upper tributary of the Rio Itiquira, Rio Paraguai basin, central Brazil, in altitude about 750 m asl (Fig. 3).

Etymology.

From the Latin, regularis (regular), a reference to the caudal fin bars in males, regularly shaped and arranged on fin.