Melanorivulus amambaiensis, Volcan, Matheus V., Severo-Neto, Francisco & Lanes, Luis Esteban K., 2018

Volcan, Matheus V., Severo-Neto, Francisco & Lanes, Luis Esteban K., 2018, Unrecognized biodiversity in a world's hotspot: three new species of Melanorivulus (Cyprinodontiformes: Rivulidae) from tributaries of the right bank of the Rio Parana basin, Brazilian Cerrado, Zoosystematics and Evolution 94 (2), pp. 263-280 : 270-272

Melanorivulus amambaiensis sp. n.

Holotype.

MCP 53150, male, 27.9 mm SL, Brazil, Mato Grosso do Sul State, near of municipality of Naviraí, first order stream of Rio Amambai, margin of BR 487 highway, 22°57 ’11” S, 54°26 ’52” W, altitude 332 m a.s.l.; M.V. Volcan & L.E.K Lanés, 14 Dec 2016.

Paratypes.

MCP 53151, 4 males, 20.9-25.9.0 mm SL (1 C&S), 10 females, 22.8-28.7 mm SL (3 C&S), all collected with the holotype. ZUFMS 5497, 1 male, 21.6 mm SL, 4 females, 22.2-22.9 mm SL, all collected with the holotype.

Diagnosis.

The presence of an orange or orange-red anal fin with grey or dark grey distal margin (vs. no similar colour pattern) and chevron-like red bars in inverted Y-shape in the flank of males (vs. no similar pattern) distinguishes the M. amambaiensis from all other species of the M. pictus species group. Additionally, the new species is distinguished by the lower caudal fin ray count (25-28 vs. 29-34), except M. faucireticulatus ; by the lower body depth in males (29.4-21.6 mm SL vs. 21.8-26.5), except from M. vittatus , M. polychromus , M. nigropunctatus , M. interruptus and M. ivinhemensis ; by a lower caudal peduncle depth in males (12.4-13.5 mm SL vs. 13.5-16.8 mm SL), except in M. polychromus , M. nigropunctatus , M. interruptus and M. ivinhemensis . Females are distinguished from M. apiamici , M. faucireticulatus , M. giarettai , M. planaltinus , M. rutilicaudus , M. scalaris , M. nigropunctatus , M. proximus , M. linearis , M. nigromarginatus and M. formosensis by the lower body depth (19.1-21.5 mm SL vs. 21.6-26.0 mm SL); and from M. apiamici , M. egens , M. faucireticulatus , M. giarettai , M. planaltinus , M. nigropunctatus , M. linearis , M. nigromarginatus and M. ofaie by a shorter pre-dorsal length (74.5-76.6 mm SL vs. 76.4-83.3 mm SL).

Description.

Morphometric data are presented in Table 3. Females larger than males, largest female examined 28.7 mm SL, largest male 27.9 mm SL. Dorsal profile slightly convex from snout to end of dorsal-fin base, straight on caudal peduncle. Ventral profile weakly convex from lower jaw to operculum. Straight from operculum to origin of pelvic-fin and in the caudal peduncle. Body slender, cylindrical and compressed, greatest body depth at origin of pelvic-fin base. Snout blunt. Jaws short.

Short dorsal and anal fins. Dorsal-fin rays 8-9. Dorsal fin slightly pointed in males, rounded in females. Dorsal-fin origin on a vertical through base of 8th or 9th anal-fin ray, and between neural spines of the 20th and 21th vertebrae. Anal-fin rays 12-14. Anal fin slightly pointed in males and females. Origin of anal fin at a vertical through pleural ribs of 15 th– 16th vertebrae. Caudal fin oval shaped, longer than deep, 25-28 rays. Pectoral fin rays 11-13. Pectoral fins rounded, with posterior margin reaching vertical at about 70-90% of length between pectoral-fin and pelvic-fin bases. Pelvic-fin rays 6-7. Posterior tip of pelvic fin reaching a vertical at slightly anterior to the anus to 1st anal-fin ray. Pelvic-fin bases in close proximity.

Scales small, cycloid. Body and head entirely scaled, except anterior ventral surface of the head. Body squamation extending over anterior 15-20% of caudal-fin base. No scales on dorsal and anal-fin bases. Frontal squamation E and F-patterned or with two patterns, one on each side (present in one specimen). E-scales not overlapping medially. Transverse row of scales anterior to H-scale; scales arranged in regular circular pattern around A-scale. A-scale without exposed margins. Longitudinal series of scales 27-31; transverse series of scales 8-9; scale rows around caudal peduncle 16. No contact organs on flank and fins.

Cephalic neuromasts: supraorbital 3+3, parietal 1, anterior rostral 1, posterior rostral 1, infraorbital 1+9 –11+1– 2, preorbital 2, otic 1, postotic 1-2, supratemporal 1, median opercular 1, ventral opercular 1-2, preopercular 2+4-5, mandibular 2-3+1, lateral mandibular 1-2, paramandibular 1. Two neuromasts on caudal-fin base.

Six branchiostegal rays. Gill rakers on first branchial arch 1+7-8. First epibranchial slightly curved. Total number of vertebrae 30-31, 13-14 precaudal vertebrae, 17 caudal vertebrae. Ventral process of angulo-articular short, pointed. Vomerine teeth 2-3. Dermosphenotic present. Second pharyngobranchial teeth absent.

Colouration in life.

Males (Fig. 8). Flank light metallic blue-whitish, sometimes purplish above anal fin; numerous oblique narrow red bars irregularly arranged, forming reticulated chevron-like marks anteriorly directed with a branching on the lower portion in inverted Y-shape, sometimes with a branching on the upper and lower portions in X-shape; between these bars one to four red dots obliquely distributed mostly on dorsal portion of flank; reddish dots on anteroventral part of flank, sometimes forming rows, mostly between bases of the pectoral and the pelvic fin; one to three oblique reddish-brown bars between the postorbital region and the pectoral fin; reddish-brown spots on the humeral region. Dorsum metallic grey or yellowish grey, venter white. Dorsal portion of head yellowish-grey; ventral portion white, without marks or any pigmentation pattern; golden iridescence on opercular region. Jaws grey to pale yellowish-grey. Iris pale yellow. Dorsal fin yellowish-hyaline with three or four oblique narrow brownish-red or red bars; basal portion pale yellow. Anal fin orange or orange-red, basal portion pale blue with reddish dots forming reticulated pattern, posterior portion pale blue sometimes with two or three reddish oblique bars, distal region grey or dark grey on the marginal border. Caudal fin hyaline or yellowish-hy aline, yellowish-orange on ventral portion; four to seven narrow oblique brownish-red or red bars cover 2/3 of caudal fin, absent in ventral portion. Pectoral fin hyaline, or yellowish-hyaline. Pelvic fin orange or yellowish-orange, sometimes with orange-brown anterior margin.

Females (Fig. 9). Flank similar to males, but more evident reddish-brown or brown spots between pectoral and pelvic fins. Numerous oblique narrow red bars irregularly arranged, forming reticulated chevron-like marks anteriorly directed, sometimes with a branching on the lower portion in inverted Y-shape. Dorsum and dorsal portion of head greenish-gray with small black dots; ventral portion of head white, with dark grey spots; golden iridescence on opercular region. Jaws greyish-brown. Iris pale yellow, sometimes bordered with grey. Dorsal fin yellowish-orange or yellowish hyaline, with three reddish-brown narrow horizontal bars forming a reticulated pattern. Anal fin orange-yellow, basal portion pale blue with reddish dots forming a reticulated pattern, posterior portion pale blue with two or three reddish oblique bars, distal region becoming gradually dark reddish brown on the marginal border. Caudal fin yellowish-orange, with three to seven grey or dark grey bars; small elongated black spot on dorso-basal portion of the fin, sometimes overlapping the most anterior bar. Pectoral fins hyaline. Pelvic fins yellowish-orange, sometimes with reddish-brown anterior margin.

Distribution.

The species is only known from its type locality, a small first order drainage and direct tributary of Rio Amambaí, state of Mato Grosso do Sul, Brazil (Fig. 3).

Etymology.

The name amambaiensis is a reference to the occurrence of the new species in the Rio Amambaí basin.

Habitat notes.

Melanorivulus amambaiensis was recorded in a small natural drainage, direct tributary of the Rio Amambaí, with depth not exceeding 50 cm and with low flow in an area totally exposed to the sun, parallel to BR 487 highway (Fig. 10). The region has a smoothly undulating terrain and the area of occurrence is at an altitude of 327 m a.s.l.. The drainage has a clayey substrate, which gives an orange colour to the water when disturbed. Only Gymnotus aff. carapo Linnaeus, 1758 was registered co-occurring with M. amambaiensis .

Conservation status.

The species is known only from its type locality. It seems to be a micro endemic of the Rio Amambaí basin, since other species occur in the adjacent basins. Part of its original area was fragmented by BR 487 and there is high frequency traffic of vehicles on this highway. Consequently, the species is subject to accidents with potentially dangerous loads, which present a threat to the population of M. amambaiensis . In addition, the surrounding region is largely degraded by agricultural activities that also threaten its habitat quality. Thus, M. amambaiensis was accounted as “Vulnerable” according to the IUCN (2012) standards. The species has an area of occurrence of less than 2000 km², occurs in only one locality and suffers from a reduction in its area of occupation and in the quality of its habitat (VU B2abii, iii).