Melanorivulus ivinhemensis, 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 : 267-270

Melanorivulus ivinhemensis sp. n.

Holotype.

MCP 53147, male, 30.1 mm SL, Brazil, Mato Grosso do Sul State, municipality of Nova Andradina , first order stream of Rio Ivinhema, 22°11 ’53” S, 53°20 ’12” W, altitude 300 m a.s.l.; M.V. Volcan & L.E.K Lanés, 09 Dec 2016.

Paratypes.

MCP 53153, 6 males, 20.3 –27.7– 31.0 mm SL, 7 females, 18.5-29.7 mm SL (1 C&S), 2 juvenile, sex undetermined, 14.0-15.4 mm, all collected with the holotype. MCP 53148, 2 juvenile, sex undetermined, 14.3-16.9 mm, wetland in the boarder of BR 376 highway, 22°21 ’22” S, 53°30 ’32” W, altitude 252 m a.s.l.; M.V. Volcan & L.E.K Lanés, 08 Dec 2016. MCP 53149, 1 male, 18.6 mm SL, 2 females, 25.7-30.4 mm SL, first order stream of Rio Ivinhema, 22°21 ’51” S, 53°39 ’42” W, altitude 310 m a.s.l.; M.V. Volcan & L.E.K Lanés, 08 Dec 2016. ZUFMS 5365, 5 males, 21.8-29.5 mm SL (3 C&S), 3 females, 18.1-20.4 mm SL, first order stream of Rio Ivinhema, 22°12 ’17” S, 53°27 ’17” W, altitude 317 m a.s.l.; T.R.F. Sinani & M.O. Bordignon, 17 Sep 2016.

Diagnosis.

Melanorivulus ivinhemensis is distinguished from all other species of the M. pictus species group by having a yellow caudal fin with thin red bars arranged only in the median region of the fin in males (vs. red bars absent or red bars extending from the ventral or median region to the dorsal region of the caudal fin), except in M. rutilicaudus . Besides, it is distinguished from all M. pictus species by the origin of the anal fin at a vertical through pleural ribs of 15th-18th vertebrae (vs. 13-15 vertebrae), except in M. amambaiensis , M. planaltinus , M. scalaris , M. polychromus , M. ofaie , M. interruptus and M. nigropunctatus ; and by the greater snout length in males (16.1-21.3 vs. 11.4-16.3), except in M. amambaiensis , M. apiamici , M. interruptus , M. vittatus , M. polychromus and M. nigropunctatus . Distinguished from M. planaltinus , M. rutilicaudus , M. interruptus by a lower caudal fin ray count (29-31 vs. 32-34) and from M. amambaiensis by a higher caudal fin ray count (29-31 vs. 25-28). Distinguished from M. faucireticulatus , M. giarettai , M. interruptus , M. leali , M. vittatus and M. formosensis by a short basihyal cartilage 10-15% of total basihyal length (vs. 20-25%). From M. interruptus , M. vittatus , M. ofaie , M. nigropunctatus , M. proximus , M. linearis and M. nigromarginatus it is distinguished by a smaller dorsal fin base length in females (8.9-10.4% vs. 10.5-14.8%). Distinguished from M. giarettai , M. proximus , M. linearis , M. nigromarginatus and M. planaltinus by lower number of gill rakers on the first branchial arch (1+7 vs 1-2+8), and from the M. pictus by the dorsal-fin origin on a vertical through base of 8th or 9th anal-fin ray (vs. on vertical through base of 7th anal-fin ray).

Description.

Morphometric data are presented in Table 2. Females usually larger than males, largest female 30.4 mm SL, largest male examined 30.1 mm SL. Dorsal profile slightly convex from snout to end of dorsal-fin base, straight on caudal peduncle. Ventral profile convex from lower jaw to origin of anal-fin, approximately straight to end of caudal peduncle. Body slender, approximately cylindrical and compressed, greatest body depth anterior of pelvic fin base, in the pelvic fin base or at the anus. Snout slightly pointed. Jaws short.

Short dorsal and anal fins. Dorsal-fin rays 7-9. Dorsal fin rounded or 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 20th and 22th 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 15th-18th vertebrae. Caudal fin oval shaped, deeper than long, 29-31 rays. Pectoral fin rays 11-13. Pectoral fins rounded, with posterior margin reaching vertical at about 60-90% of the length between pectoral-fin and pelvic-fin bases. Pelvic-fin rays 6-7, one individual with one single pelvic fin. Posterior tip of pelvic fin reaching vertical between anus to 2nd anal-fin ray. Position of pelvic-fin bases variable, in close proximity, or with bases separated by a great distance, similar to the size of the base of the pelvic fin.

Scales small, cycloid. Body and head entirely scaled, except anterior ventral surface of head. Body squamation extending over anterior 15-25% 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 in one specimen. E-scales generally not overlapping medially. In one specimen E-scales marginally overlapped. Transverse row of scales anterior to H-scale; scales arranged in regular circular pattern around A-scale. A-scale usually without exposed margins, four specimens with posterior margin exposed, overlapping the B-scale. Longitudinal series of scales 29-31; 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+11-12+1, preorbital 2, otic 1, postotic 1-2, supratemporal 1, median opercular 1, ventral opercular 1-2, preopercular 2+4-6, mandibular 3-4+1, lateral mandibular 1-2, paramandibular 1. Two neuromasts on caudal-fin base.

Six branchiostegal rays. Gill rakers on first branchial arch 1+7. First epibranchial slightly curved. Total number of vertebrae 29-31, 14 precaudal vertebrae, 15-17 caudal vertebrae. Ventral process of angulo-articular short, pointed. Vomerine teeth 2-5. Dermosphenotic present. Basihyal sub-triangular, greatest width 45-50% of length; basihyal cartilage 10-15% of total basihyal length. Second pharyngobranchial teeth absent.

Colouration in life.

Males (Fig. 5). Metallic greenish-gray flank, purple-blue close to anal fin; red dots on anterior flank area, sometimes few red dots on the anteroventral region; one to three oblique narrow bars between the medial pectoral fin portion and close to the pelvic fin base, sometimes one or two of these bars forming chevron-like marks with an angle on the ventral region of the flank; 7-9 oblique narrow red bars anteriorly directed, forming chevron-like marks with an angle on midline of flank, and generally positioned posteriorly to the pelvic fin base on the caudal peduncle. Two parallel and oblique dark brown bars often interconnected by a brown-dark horizontal line between postorbital and posterior opercular region, sometimes forming a broad and well-defined mid-lateral dark stripe between postorbital region and area above the pectoral fin at mid length. Yellowish-grey dorsum with small black dots, venter white. Dorsal portion of the head yellowish-grey sometimes with small black dots; ventral portion white; golden iridescence on opercular region. Dark grey jaws varying to pale yellowish-grey. Iris pale yellow. Dorsal fin yellow with three or five oblique narrow red bars on posterior portion of fin. Anal fin yellow or orange-yellow, sometimes with a distal dark margin, basal portion light metallic blue-whitish, posterior portion pale blue with two or three faint reddish oblique bars. Caudal fin yellow or hyaline-yellowish, presenting three to six vertical or slightly oblique parallel red or red brownish bars in the central region. Pectoral fin yellowish hyaline. Pelvic fin yellowish hyaline or orange and hyaline, sometimes with a distal dark margin.

Females (Fig. 6). Flank similar to males. Dorsum and dorsal portion of head greenish-gray with small black dots; ventral portion of head white, with black marks, sometimes inconspicuous; pale golden iridescence on opercular region. Jaws pale yellowish-grey. Iris pale yellow, sometimes with dark brown bars on anterior and posterior portions. Dorsal fin yellowish-orange, with horizontally elongated dark brown to black spots or bars in the medial region; dark grey narrow margin delineating entire dorsal fin. Anal fin yellowish-orange, basal portion pale blue with two interrupted reddish bars, posterior portion pale blue with two or three reddish oblique bars, distal region becoming gradually dark reddish brown on marginal border, distal margin with high concentration of melanophores. Caudal fin orange, sometimes orange and hyaline in central portion, with three to six dark brown to black bars, sometimes bars formed by dense, vertically elongated spots, the rays and inter-spaces between them pigmented; dark brown to black circular or sub triangular spot on dorso-basal portion of the caudal fin; dark grey margin. Pectoral fins hyaline. Pelvic fins orange-yellow, with a reddish-brown anterior margin.

Distribution.

Melanorivulus ivinhemensis is so far only known from first order streams and small wetlands associated with both margins of the lower course of the Rio Ivinhema, Rio Paraná basin (Figure 3).

Etymology.

The name ivinhemensis is a reference to the occurrence of the new species in the Rio Ivinhema basin.

Habitat notes.

Melanorivulus ivinhemensis was recorded in marginal areas of small first order streams and in wetlands completely exposed to the sun on a slightly undulating terrain at altitudes ranging from 267 to 315 m a.s.l. (Fig. 7). One wetland was deep (about 70 cm of maximum depth), with muddy substratum and turbid water (Fig. 7b), while in the other localities the species was recorded in shallow areas, not exceeding 20 cm depth, in crystalline waters and with a clayey substrate (Fig. 7a, c). Eight fish species were recorded co-occurring with M. ivinhemensis : Aphyocharax dentatus Eigenmann & Kennedy, 1903, Pyrrhulina australis Eigenmann & Kennedy, 1903, Hyphessobrycon anisitsi (Eigenmann, 1907), Hyphessobrycon eques (Steindachner, 1882), Serrapinnus kriegi (Schindler, 1937), Cichlasoma dimerus (Heckel, 1840), Hoplerythrinus unitaeniatus (Spix & Agassiz, 1829) and Moenkhausia sanctaefilomenae (Steindachner, 1907).

Conservation status.

The new species is endemic of Rio Ivinhema and was recorded in four different areas, in a range of about 25 km along both sides of the river and there is a large density of potential environments for its occurrence along this stretch. It has been recorded in areas with no major impacts - although under intense agricultural activity - and therefore there is no evidence that the species is threatened with extinction.