Melanorivulus proximus, 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 : 17-19

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

Rivulus pictus (non Rivulus pictus Costa, 1989); Costa 1995: 216 (misidentification).

Rivulus scalaris (non Rivulus scalaris Costa, 2005); Costa 2005: 79 (misidentification).

Holotype

UFRJ 11681, male, 27.7 mm SL; Brazil: Mato Grosso do Sul state: Cassilândia municipality: stream crossing the road MS-306, Rio Aporé drainage, Rio Paraná Basin, 19°03 ’54” S, 51°49 ’56” W, altitude about 515 m asl; W.J.E.M. Costa et al., 20 Sep. 2011.

Paratypes

All from Brazil: Rio Aporé drainage, upper Rio Paraná Basin. Mato Grosso do Sul state: UFRJ 10792, 4 males, 25.6-30.0 mm SL, 1 female, 25.6 mm SL; UFRJ 10793, 1 male, 23.6 mm SL, 1 female, 21.1 mm SL (C&S); collected with holotype. - UFRJ 10788, 6 males, 15.7-27.7 mm SL, 4 females, 24.0-27.4 mm SL; UFRJ 10789, 3 males, 20.9-21.9 mm SL, 2 females, 18.5-20.0 mm SL (C&S); CICCAA 00692, 5 males, 21.9-25.8 mm SL, 5 females, 21.7-25.6 mm SL; Cassilândia municipality: road MS-306, 19°02 ’15” S, 52°01 ’57” W, altitude about 540 m asl; W.J.E.M. Costa et al., 20 Sep. 2011.- UFRJ 2207, 8 males, 20.2-27.1 mm SL, 12 females, 17.8-35.4 mm SL.; UFRJ 2280, 1 male, 25.9 mm SL, 2 females, 27.9-28.7 mm SL (C&S); Cassilândia municipality: swamp close to Ribeirão Grande, road MS-306, about 30 km SE from the town of Cassilândia, 19°15 ’40” S, 51°30 ’03” W, altitude about 495 m asl; W.J.E.M. Costa et al., 17 Sep. 1994. Goiás state: UFRJ 10821, 1 male, 27.7 mm SL, 1 female, 22.7 mm SL; UFRJ 10822, 4 males, 15.6-18.4 mm SL, 12 females, 16.2-22.1 mm SL; Itajá municipality: Ribeirão Bagageiro, road GO-302, 19°06 ’17” S, 51°42 ’15” W, altitude about 455 m asl; W.J.E.M. Costa, B.B. Costa & C.P. Bove, 15 Jan. 2007.

Additional material (non-types)

UFRJ 10819, 12; Brazil: Goiás state: Itajá municipality: road GO-302, 19°05 ’09” S, 51°36 ’27” W, altitude about 440 m asl; W.J.E.M. Costa et al., 20 Sep. 2011.

Diagnosis. Melanorivulus proximus is distinguished from all other congeners of the M. pictus group except M. scalaris by the presence of irregularly arranged, interconnected oblique red bars on flank, forming Y- and X-shaped marks. Melanorivulus proximus is distinguished from M. scalaris by: caudal fin base colour pale orangish pink in females (vs. pale yellow); dorsal and anal fin sharply pointed in males (vs. rounded to moderately pointed), dorsal-fin origin at vertical between base of 9th and 10th (vs. between base of 7th and 8th); longitudinal series of scales 29-30 (vs. 31-34); pre-dorsal length longer in males (75.9-78.4 % SL vs. 73.0-75.0 % SL); longer anal-fin base (21.1-24.7 % SL in males and 18.8-21.4 % SL in females vs. 18.1-21.0 % SL in males and 16.2-18.5 % SL in females); and fewer infraorbital neuromasts around orbit (9-10 vs. 11-12).

Description

Morphometric data appear in Table 1. Body relatively deep, subcylindrical anteriorly, slightly 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, approximately straight on caudal peduncle. 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 2 + 7-8.

Dorsal and anal fins short, sharply pointed in males, rounded to slightly pointed in females. Caudal fin rounded, slightly longer than deep. Pectoral fin rounded, posterior margin reaching vertical at about 90 % of length between pectoral-fin and pelvic-fin bases. Pelvic fin small, longer in males, tip reaching between base of 2nd and 3rd anal-fin rays in males, reaching anus in females; pelvic-fin bases medially in close proximity. Dorsal-fin origin at vertical between base of 9th and 10th anal-fin rays. Dorsal-fin rays 9-11; anal-fin rays 13-15; caudal-fin rays 30-32; 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 20th vertebrae; first proximal radial of anal fin between pleural ribs of 13th and 14th 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, anal and pectoral-fin bases. Frontal squamation E-patterned; E-scales not overlapping medially; scales arranged in regular circular pattern around A-scale without exposed margins; transverse row of scales anterior to H-scale. Five supraorbital scales. Longitudinal series of scales 29-30; transverse series of scales 8; 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 + 9-10 + 1, preorbital 2, otic 1, post-otic 2, supratemporal 1, median opercular 1, ventral opercular 1, preopercular 2 + 4, mandibular 3 + 1, lateral mandibular 2-3, paramandibular 1. Lateral line interrupted, alternating sets of 3-4 scales with one neuromast and without neuromasts. Two neuromasts on caudal-fin base.

Colouration in life

Males. Flank metallic greenish blue to bright blue, with narrow oblique red bars between humeral region and posterior portion of caudal peduncle; bars irregularly arranged, forming chevron-like marks with angle varying in position on flank, often connected to short adjacent bars, forming Y- and X-shaped marks; 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, often coalesced to form zigzag red marks. Dorsolateral portion of body, between posterior part of head and anterior part of flank, above humeral region, pale golden. Humeral region with horizontally elongated black spot. Dorsum light brown, venter white. Opercular region greenish golden with dark red reticulation on scale margins; suborbital region yellowish white; lower jaw dark grey. Iris pale yellow, with dark brown bar on anterior and posterior portions. Dorsal fin bluish white, sometimes yellowish on distal portion, with 4-5 transverse, narrow faint red or red stripes. Anal fin pale yellow, base and posterior portion bluish white with row of light red dots or short stripes. Caudal fin pale yellow to bluish white, with 5-6 narrow red or reddish orange stripes. Pectoral fin yellowish hyaline. Pelvic fin orangish pale yellow.

Females. Similar to males, except flank base colour pale greenish golden; dorsal and caudal fin bars dark grey; caudal fin base colour pale orangish pink; and pres ence 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

Middle section of the Rio Aporé drainage, upper Rio Paraná Basin, central Brazil (Fig. 3).

Etymology

From the Latin proximus (near, neighbour), referring to its distribution area at the same drainage as M. scalaris .