Melanorivulus linearis, 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 : 22-23

Melanorivulus linearis sp. n. Figs 6, 7, Table 3

Holotype

UFRJ 11678, male, 25.1 mm SL; Brazil: Mato Grosso do Sul state: Bandeirantes municipality: Córrego Água Limpa, upper Rio Pardo drainage, Rio Paraná basin, 19°40 ’01” S, 54°18 ’13” W, altitude about 620 m asl; W.J.E.M. Costa, B.B. Costa & C.P. Bove, 12 Jan. 2004.

Paratypes

UFRJ 11679, 2 males, 27.9-30.1 mm SL, 7 females, 15.8-23.7 mm SL; UFRJ 11680, 2 males, 20.8-26.0 mm SL, 2 females, 19.5-21.1 mm SL (C&S); CICCAA 00694, 2 males, 19.0-27.2 mm SL, 3 females, 19.6-20.5 mm SL; collected with holotype.

Diagnosis

Melanorivulus linearis is similar to M. egens , and distinguished from all other species of the M. pictus group by the presence of red chevron-shaped marks regularly distributed on the flank (vs. irregularly), absence of distinctive dark marks on humeral region (vs. presence), and absence of red dots on the anteroventral portion of flank (vs. presence). Melanorivulus linearis is distinguished from M. egens by the presence of red bars restricted to the dorsal portion of the caudal fin in males (vs. absence), presence of black bars on the caudal fin in females (vs. black dots); presence of a pale green spot on humeral region in males (vs. absence); and second proximal radial of the dorsal fin between neural spines of 18th and 19th vertebrae (vs. between neural spines of 19th and 21st vertebrae).

Description

Morphometric data appear in Table 3. 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 3-5. 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 base of 2nd or 3rd 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 or 9th anal-fin ray. Dorsal-fin rays 10-11; anal-fin rays 13-15; caudal-fin rays 31-32; pectoral-fin rays 13-14; pelvic-fin rays 7. No contact organs on fins. Second proximal radial of dorsal fin between neural spines of 18th and 19th vertebrae; first proximal radial of anal fin between pleural ribs of 13th and 15th vertebrae; total vertebrae 30-31.

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 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 + 9-11 + 1, preorbital 2, otic 1, post-otic 1-2, 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 greenish blue, sometimes purplish blue above anal fin, with oblique narrow red bars between humeral region and posterior portion of caudal peduncle; bars regularly arranged, forming chevron pattern directed anteriorly, with angle on flank midline or above it; bars with minute vertical extensions on each scale margin; dorsal portion of flank with few red dots; anteroventral portion of flank without red marks; pale green spot on humeral region. Dorsum light brown, venter white. Side of head light brown on dorsal portion, yellowish white on ventral portion to pale golden on opercle; melanophores dispersed, not forming distinct marks on post-orbital region; lower jaw dark grey. Iris pale yellow, sometimes with dark brown bar on anterior and posterior portions. Dorsal fin light yellow, with four to six oblique red bars through whole fin. Anal fin yellowish orange, basal portion purplish white with six or seven short red bars, distal margin black. Caudal fin light yellow, with six to eight narrow red bars extending between dorsal and middle portions of fin; fin margin dark grey. Pectoral fin hyaline. Pelvic fin light yellow with narrow black margin.

Females. Similar to males, except flank base colour pale greenish golden; no distinct marks on humeral region; dorsal and caudal fin bars dark grey to black; caudal fin base colour pale white; absence of pale green spot on humeral region; and presence of triangular 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.

Distribution

Known only from the type locality, upper section of the Rio Pardo, middle Rio Paraná Basin, central Brazil (Fig. 3).

Etymology

From the Latin, linearis (consisting of lines), an allusion to the red oblique lines regularly arranged on the flank in males.