Melanorivulus larissae Ywamoto & Nielsen & Oliveira 2020, new species

Melanorivulus larissae, new species

(Figs. 1-2; Table1)

Holotype. ZUEC 17154, male, 23.4 mm SL: Brazil, São Paulo, Ouroeste, Ribeirão Santa Rita, tributary of Rio Grande, Rio Paraná basin, 19°59’56’’S, 50°22’55”W, altitude 494 m; Daniel Sobral dos Santos, 12 May 2017.

Paratypes. ZUEC 17155 (5 males, 21.0– 26.9 mm SL, 5 females, 21.1–26.1 mm SL, 2 C&S); MZUSP 123086 (1 male 22.1 mm, 1 female 22.0 mm); LBP 29539 (1 male, 23.1 mm SL; 1 female, 22.7 mm SL); collected with the holotype.

Diagnosis. Melanorivulus larissae is distinguished from all other species of Melanorivulus, except from those belonging to the M. pictus species group, by two color pattern features, i.e., sides of body light greenish gray above the anal fin base in males and presence of an irregular black stripe between the postorbital region and the mid-length of the pectoral fin in both sexes. Melanorivulus larissae is distinguished from all other species of the M. pictus species group by sides of body light bluish gray in males (vs. greenish blue or greenish gold), 10–12 oblique red bars, 8 of which chevron-like, bifurcated and complete, i.e., running from dorsum to ventral area, and 2–4 incomplete bars, at the sides of body (vs. 8 oblique red lines at the sides of body in M. ofaie; 9–10 in M. egens, M. faucireticulatus, M. scalaris and M. vittatus, 16 in M. rutilicaudus, thick red lines in M. scalaris, M. litteratus, M. ofaie, M. planaltinus, and M. vittatus), and caudal fin in males light yellow, with 3–4 irregular vertical red lines (vs. never a similar color pattern).

Melanorivulus larissae is also distinguished from other species of M. pictus species group by lower caudal fin length in males (23.9–28.0% SL vs 29.4–39.8% SL, except from M. planaltinus, M. ofaie, and M. polychro- mus), and females (24.5–29.6% SL vs 30.6–38.9% SL; except in M. giarettai, M. ofaie, M. nigropunctatus, and M. polychromus), lower head length in females (24.3–28.6% SL vs 28.7–38.9% SL, except in M. leali and M. pictus), greater snout length in males (20.3–28.7% SL vs 11.4-17.1% SL, except M. ofaie), and females (19.6–23.0% SL vs 11.4–18.5% SL, except M. nigropunctatus), and by a lower number of vertebrae (28–29 vs. 30–32 except M. apiamici, M. litteratus, M. rutilicaudus, M. scalaris, M. egens, and M. interruptus), and lower number of pelvic-fin rays (6 vs. 7–8 except M. giarettai, M. planaltinus, M. nigropunctatus, M. polychromus, and M. nigromarginatus), in both sexes.

Additionally, M. larissae differs from M. giarettai, M. vittatus, M. polychromus, M. egens, M. proximus, M. amambaiensis, M. faucireticulatus, M. ivinhemensis, and M. leali by a lower number of caudal fin rays (28–30 vs. 31–34). It can be distinguished from all remaining species of the M. pictus species group, except in M. planaltinus, M. leali, and M. pictus, by the presence of rounded dorsal fin in both sexes (vs. slight pointed or pointed dorsal fin), by higher caudal-fin rays counts (32–33 vs. 28–31 in M. amambaiensis, M. apiamici, M. egens, M. faucireticulatus, M. ivinhemensis, and M. leali); by anal-fin origin between pleural ribs of 15 th and 16 th vertebrae (vs. 13 th and 15 th vertebrae in M. egens, M. faucireticulatus, M. leali, M. litteratus, M. rutilicaudus, and M. formosensis); by dorsalfin origin on vertical through base of 8 th anal-fin ray (vs. vertical through base of 7 th or 9 th- 10 th anal-fin ray in M. apiamici, M. egens, M. faucireticulatus, M. pictus, M. polychromus, and M. proximus).

Description. Morphometric data presented in Table 1. Largest male examined 26.9 mm SL, largest female examined 26.1 mm SL. Dorsal profile gently convex from snout to end of dorsal-fin base, approximately straight along caudal peduncle. Ventral profile slightly convex from lower jaw to anal-fin origin, approximately straight along caudal peduncle. Body slender, compressed, greatest body depth at level of pelvic fin base. Snout pointed in lateral view. Jaws short.

Short dorsal and anal fins; rounded in males and females, without filaments in both sexes. Caudal fin oval shaped, longer than deep. Pectoral fin rounded, with its posterior margin reaching 60% of the distance between pectoral and pelvic fins bases. Pelvic fin elliptical, short, its tip reaching the first anal fin ray base in males and uro- genital papilla in females. Pelvic fin bases in close proximity medially. Dorsal-fin origin at vertical through base of 9th anal-fin ray in males and females at the level of the 21 th vertebra. Anal-fin origin at the 16 th vertebra. Dorsal-fin rays 9–10; anal-fin rays 13–14; caudal-fin rays 28–30; pectoral-fin rays 12; pelvic-fin rays 6. No scales on dorsal and anal-fin bases.

TABLE I. Morphometric and selected meristic data for the holotype (H) and paratypes of Melanorivulus larissae. SD = standard deviation.

Scales cycloid. Frontal squamation E-patterned; E-scales not overlapping. Longitudinal series of scales 27–30; transverse series of scales 8; scale rows around caudal peduncle 16. No contact organs on scales and fin rays. Cephalic neuromasts: supraorbital 3 + 3, parietal 1, posterior rostral 1, infraorbital 1 + 10 + 1, preorbital 1, otic 1, post-otic 1, supratemporal 1, median opercular 1, ventral opercular 1, preopercular 2 + 4, mandibular 3 + 1, lateral mandibular 2, paramandibular 1. Two neuromasts on caudal-fin base. Six branchiostegal rays. Gill-rakers on first branchial arch 1 + 7. Vomerine teeth 2. Total vertebrae 28-29.

Color in life. Males (Fig. 1). Sides of body bluish light gray, with 12–13 oblique red bars, 3–4 centralmost forming chevron-like rows, branching at midline, with forward-pointing vertices at midline, remaining bars simple, some males presenting X-shaped red bars. Caudal peduncle presenting small, roughly square-shaped red blotches, juvenile males presenting very small black spot at the upper portion of the caudal peduncle. Anteroventral portion of flank white, long dark longitudinal stripe with irregular shape extending between opercular area and first red chevron-like bar. Dorsum light brown. Venter whitish. Sides of head light brown, opercular region light yellow with golden tint and irregular dark stripes. Jaws light brown. Iris pale yellow. Dorsal fin light yellow, with 2–3 irregular, oblique brown lines. Anal fin middle portion light yellow, basal area light blue, with short narrow red bars, and distal portion with black margin. Caudal fin light yellow, with 3–4 irregular, vertical red bars. Pelvic fin light yellow with light blue pigmentation at basis and black margin at distal portion. Pectoral fin hyaline.

Females (Fig. 2). Sides of body light brown, with 9–10 dark red oblique bars, forming a chevron-like pattern, chevron vertices at lateral midline and pointing forward to the head. Irregular first vertical lines overlapping with long longitudinal dark stripe with irregular shape extending from postorbital region to anterior portion of trunk. Opercular area golden, with irregular dark blotches. Dorsum light brown, presenting scattered dark spots. Venter white. Jaws brown. Iris pale orange, anterior and posterior edges of eye dark brown. Dorsal fin hyaline, with two irregular, oblique dark lines. Anal fin with basal portion light blue, and distal portion with a black margin. Caudal fin hyaline, with 3–5 grey vertical bars; black spot on its dorsal portion. Pectoral and pelvic fins hyaline.

Distribution and habitat. The new species is known only from the type-locality, a stream tributary of Ribeirão Santa Rita, itself a tributary of Rio Grande, Rio Paraná basin, northwestern São Paulo state, Brazil (Fig. 4). The type locality is a small headwater, first order stream, located in the surroundings of the city of Ouroeste, São Paulo, Brazil. The stream has clear water, with maximum depth of 5 cm. The stream channel is hidden by grasses and sedges (Fig. 3).

Etymology. Named in honor of Larissa da Silva Sobral, daughter of the discoverer of the species.