Rhinopetitia paucirastra, Menezes & Netto-Ferreira, 2019

Menezes, Naércio A. & Netto-Ferreira, Andre L., 2019, A systematic review of Rhinopetitia Géry (Teleostei, Characiformes, Characidae) with descriptions of four new species and redescription of R. myersi Géry, Zootaxa 4700 (1), pp. 59-86 : 68-71

Rhinopetitia paucirastra , new species

Figs. 10–13 , Table 2 .

Holotype. MZUSP 124118 , female 32.0 mm SL, Brazil, Goiás, Minaçu, right bank tributary of Rio Tocantizinho, Serra da Mesa , 14°08’46”S, 48°02’52”W, March 2006, O.T. Oyakawa & K.C. Mautari.

Paratypes. All from Brazil, Goiás . INPA 59017 , 4 (28.0–30.0 mm SL) , MNRJ 51533 , 4 (30.0–33.0 mm SL) , MPEG 38601 , 4 (30.0–32.0 mm SL) , MZUSP 95063 , 44 (25.0–39.0 mm SL, 5 C&S, 29.0–39.0 mm SL) , UFRGS 27590 , 4 (30.0–33.0 mm SL), collected with the holotype ; MZUSP 77477 , 1 male (31.0 mm SL), upstream of ponte do Rubão, Serra da Mesa , about 13°50’S, 48°18’W, November 1996, D.F. Moraes, A. Akama & O.T. Oyakawa .

Diagnosis. Rhinopetitia paucirastra can be distinguished from its congeners by having fewer gill rakers on the external part of first gill arch (8–12, vs 13–19) and the outer row premaxillary teeth with 3 cusps vs 4 to 5 ( Figs. 3 and 11 ). Aditionally it has the body deeper than R.oligolepis and R. nigrofasciata (body depth 27.0–31.8 % of SL vs 19.2–24.0% of SL and 20.0–24.8 of SL respectively, Fig. 4 , Tables 3–5).

Description. Morphometrics of holotype and paratypes in Table 2 . Body small (largest examined specimen 39.0 mm SL). Head and body elongate and laterally compressed; greatest body depth at dorsal-fin origin. Profile distinctly convex from upper jaw to posterior nostril, slightly convex from latter point to dorsal-fin origin, straight along dorsal-fin base, nearly straight to slightly concave from latter point to adipose-fin origin, and concave from latter point to anteriormost dorsal procurrent ray. Ventral body profile convex from tip of lower jaw to isthmus, nearly straight from that point to vertical through pectoral-fin origin, convex from latter point to pelvic-fin origin, and straight from that point to anal-fin origin. Ventral profile along anal-fin base straight and concave on caudal peduncle.

Mouth sub-terminal to nearly inferior; lower jaw short, included in upper jaw when mouth closed. Posterior tip of maxilla reaching vertical through anterior border of pupil. Outer premaxillary tooth row with 4 (11), 5 (42*), or 6 (14) teeth, each with three cuspidate teeth, inner row with 4 (67) three to five (5) cuspidate teeth ( Fig. 11 ). Maxillary ( Fig. 11 ) with 2 (4), 3 (51*), 4 (11), or 5 (1) anterior larger teeth with five cusps (5), smaller posterior teeth with 3 to 4 cusps (5). Dentary ( Fig. 11 ) with 4 (67*) anterior large five cuspidate (5), followed by 2 (2), 3 (13), 4 (36*), 5 (15) or 6 (1), 3 to 5 five cuspidate teeth (5), gradually decreasing in size posteriorly. First gill arch with external and internal rows of gill rakers; external row with 8 (2), 9 (16), 10 (22), 11 (16*), or 12 (10) gill rakers. Branchiostegal rays 4 (5), 3 originating on anterior and 1 on posterior ceratohyal.

Scales cycloid. Lateral line complete; perforated scales 33 (6), 34 (23), or 35 (28*). Predorsal scales 11 (30), 12 (33*), 13 (2), or 14 (2). Scale rows between lateral line and dorsal-fin origin 5 (67); rows between lateral line and pelvic-fin origin 4 (67); circumpeduncular scales 12 (53*), or 13 (12). Single series of scales with sinuous posterior borders forming sheath along base of all anal-fin rays.

Pectoral-fin rays i,10 (12), 11 (40*), 12 (15). Distal tip of longest pectoral-fin ray not reaching pelvic-fin origin. Pelvic-fin rays i,6,i (67), tip of fin falling short of anal-fin origin. Supraneurals 5 (2), or 6 (3) rod shaped, or with discrete enlargement of dorsal portion; last supraneural located anterior to spines of 9 th (2) or 10 th (3) vertebral centra. Dorsal-fin rays ii,7, i, (67) First dorsal-fin pterygiophore inserting behind neural spines of 11 th vertebral centra (5). Distal margin of extended dorsal fin straight to slightly convex. Dorsal-fin origin closer to caudal-fin base than to snout tip. Base of last dorsal-fin ray situated slightly anterior to vertical through anal-fin origin. Anal-fin rays iv–v,15 (11), 16 (36), 17 (18*), or 19 (1), posteriormost ray adnate. Anal fin with short, inconspicuous, anterior lobe including last unbranched ray plus first 6–7 branched rays. Distal margin of anal fin slightly concave. First anal-fin pterygiophore inserting behind haemal arch of centra 16 th (3), or 17 th (2). Adipose fin present. Principal caudal-fin rays 10/9, (67). Dorsal and ventral procurrent rays 9 (2), 10 (2), 11 (1), or 8 (1), 9(3) and 10(1) respectively. Vertebrae 34 (4), and 35 (1).

Color in alcohol. Ground color pale to yellowish brown. Small dark chromatophores around mouth extends laterally to tip of maxilla and up toward top of head and back until the supraoccipital spine, less evident on top of fontanel; slightly larger dark chromatophores on upper portion of preopercle and fourth, five and sixth infraorbital bones and upper and median portions of opercle; lower part of opercle with scattered dark chromatophores. Small dark chromatophores all over upper part of body above lateral line scattered on lower part of body below lateral line. Mid-dorsal and adjacent longitudinal scale rows densely pigmented with small dark chromatophores distributed over whole scales, but leaving an unpigmented area near the border of each scale. Mid-line of predorsal scales with larger chromatophores.

An inconspicuous dark mid-lateral stripe in freshly preserved specimens from about vertical line through dorsal-fin origin to caudal base somewhat enlarged over caudal peduncle. A vertically elongate dark humeral blotch occupying 5 longitudinal scale rows vertically and becoming narrower downward.

All fins hyaline with scattered dark chromatophores on dorsal, caudal, and anal fins and very few on pectorals, and pelvic fins.

Sexual dimorphism. Anal fin of sexually mature males ( Fig. 12 ) with bilateral hooks on fourth largest unbranched ray and first four branched rays. Pelvic fins of sexually mature males with hooks on third to fifth branched rays ( Fig. 13 ).

Etymology. The species name paucirastra is from the Latin paucus, meaning few, rastrum meaning raker in allusion to the reduced number of gill rakers on the anterior external portion of first gill arch in comparison with the other species of the genus.

Distribution. This species is known from small tributaries draining into Rio Tocantins many of which disappeared during the construction of the Serra da Mesa dam in the upper Rio Tocantins, Goiás, Brazil ( Fig. 9 ).

Figures

FIGURE 3. (a) Rhinopetitia myersi, MZUSP 105536, male, 34.0 mm SL, and (b) R. paucirastra, MZUSP 95063, female, 32.0 mm SL. Lateral view (left side) of first gill arches displaying gill rakers.

FIGURE 4. Body depth as a function of standard length for the species of Rhinopetitia.

FIGURE 9. Map of northern South America showing collecting sites and type localities (star symbols) of the species of Rhinopetitia. Red, R. myersi; white, R. paucirastra; light blue, R. oligolepis; yellow, R. nigrofasciata; green, R. melanohumeralis. Some symbols may represent more than one locality.

FIGURE 10. Rhinopetitia paucirastra, new species, MZUSP 124118, holotype, female, 32.0 mm SL, Brazil, Goiás, Minaçu, Serra da Mesa, Rio Tocantins.

FIGURE 11. Rhinopetitia paucirastra, MZUSP 95063, 30.0 mm SL C&S, jaws and dentition, lateral view, left side, anterior at left.

FIGURE 12. Rhinopetitia paucirastra, MZUSP 95063, 30.0 mm SL C&S sexually mature male; anal-fin rays, lateral view, left side, showing anal-fin hooks.

FIGURE 13. Rhinopetitia paucirastra, MZUSP 95063, 30.0 mm SL C&S sexually mature male; pelvic-fin rays, ventral view, left side, showing pelvic-fin hooks.