Rhinopetitia myersi myersi Géry, 1964, Gery, 1964

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: 62-67

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https://doi.org/10.11646/zootaxa.4700.1.3

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Rhinopetitia myersi myersi Géry, 1964
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Rhinopetitia myersi myersi Géry, 1964  

Figs. 1–8 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 View FIGURE 8 , Table 1

Specimens examined: Holotype. MHNG 2229.03 View Materials (ex-Géry coll. M.194,1), 30.4 mm SL. Brazil, [Tocantins], Ilha do Bananal, Rio Araguaia [aproximately 10°50’S, 50°17’W], July 1959, H. Schultz. GoogleMaps  

Additional specimens. MZUSP 31861 View Materials , 30560 View Materials , 36047 View Materials , 5 View Materials (29.0–40.0 mm SL), Pará, Rio Itacaiunas, Serra dos Carajás , approximately 6°16’S, 50°32’W, M. Goulding, November, 1983 GoogleMaps   ; MZUSP 105536 View Materials , 12 View Materials (33.0–36.0 mm SL), Marabá, Rio Tapirapé , 5°36’47”S, 50°26’42”W, I. Fichberg & J. Muriel-Cunha, August 8, 2008 GoogleMaps   ; MZUSP 107020 View Materials , 4 View Materials (17.5–21.0 mm SL), Parauapebas, Rio Paraupebas, tributary of Rio Tocantins, 6°9’53”S, 49°54’32”W, M. Loeb & H. Varella, January, 2010 GoogleMaps   ; MZUSP 84165 View Materials , 10 View Materials (35.0–39.0 mm SL, 5 C&S, 30.0–39.0 mm SL), Tocantins, Porto Alegre do Tocantins, Rio Manuel Alves da Natividade , 11°36’41”S, 47°2’39”W, C.R. Moreira, J.C. Nolasco & M. Avila, July, 2002 GoogleMaps   .

Diagnosis. Rhinopetitia myersi   can be distinguished from most congeners (except R. oligolepis   and R. pauci- rastra) by the presence of 32–34 scales on the lateral line series and 12 circumpeduncular scales (vs. LL = 35–38 in R. melanohumeralis   , 35–39 in R. nigrofasciata   , and 36–38 in R. potamorhachia   ; circumpeduncular scales 13–14 in the three aforementioned species). R. myersi   differs from R. paucirastra   in having 13–17 external gill rakers on the first gill arch (vs. 8–12), from R. oligolepis   by the presence of 5 longitudinal series of scales between dorsal-fin origin and lateral line (vs. 4).

Description. (Meristic data of holotype extracted from Géry,1964). Morphometrics of recently collected specimens presented in Table 1. Body small (largest examined specimen 40 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 or slightly concave 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 orbit. Outer premaxillary tooth row with 4 (3), 5 (18), 6 (9) or 7 (1), each with five cuspidate teeth (5), inner row with 4 (31), five cuspidate teeth ( Fig. 6 View FIGURE 6 ). Maxillary ( Fig. 6 View FIGURE 6 ) with 2 (9), or 3 (18) teeth, anterior larger teeth with five cusps, smaller posterior teeth with 3 cusps (5). Dentary ( Fig. 6 View FIGURE 6 ) with 4 (31), anterior large five cuspidate teeth (5), followed by 3 (9), 4 (15), or (7) smaller five to four cuspidate teeth (5), gradually decreasing in size posteriorly. First gill arch with external and internal rows of gill rakers; external row with 13 (4), 14 (5), 15 (9), 16 (11), or 17 (2) gill rakers. Branchiostegal rays 4 (5), 3 originating on anterior and 1 on posterior ceratohyal.

Scales cycloid. Lateral line complete; perforated scales 32 (2), 33 (5), or 34 (22). Predorsal scales 10 (1), 11 (21*), or 12 (8). Scale rows between lateral line and dorsal-fin origin 5 (31); rows between lateral line and pelvicfin origin 3 (4*), or 4 (23); circumpeduncular scales 12 (29). Single series of scales with sinuous posterior borders forming sheath along base of all anal-fin rays.

Pectoral-fin rays i,10 (12), i,11 (19), or i,12 (10). Distal tip of longest pectoral-fin ray not reaching pelvic-fin origin. Pelvic-fin rays i,6,i (29), tip of fin falling short of anal-fin origin. Supraneurals 5 (5), rod shaped, or with discrete enlargement of dorsal portion; last supraneural located anterior to neural spines of 8 th (4) or 9 th (1) vertebral centra. Dorsal-fin rays ii,7, i, (31). First dorsal-fin pterygiophore inserting behind neural spines of 11 th (4) or 12 th (1) vertebral centra. Distal margin of extended dorsal fin straight to slightly convex. Dorsal-fin origin closer to caudalfin 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 (6), 16 (13), 17 (8), or 18 (1), posteriormost ray adnate. Anal fin with short, inconspicuous, anterior lobe including last unbranched ray plus first 5–6 branched rays. Distal margin of anal fin 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 (31). Dorsal and ventral caudal-fin procurrent rays 10 (2), 11 (3) or 10 (3), 11 (2) respectively. Vertebrae 33 (1), 34 (3), or 35 (1).

Color in alcohol. Ground color pale to yellowish brown. Small dark chromatophores around mouth extends laterally to tip of maxilla and up towards 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.

A dark midlateral 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 4 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 with bilateral hooks on fourth largest unbranched ray and first through fourth branched rays ( Fig. 7 View FIGURE 7 ) Mature males of R. myersi   with bilateral hooks on all branched rays of pelvic fin ( Fig. 8 View FIGURE 8 ). Hooks absent on fins of mature females.

Distribution. Rhinopetitia myersi   is known from the Ilha do Bananal, Rio Araguaia and the upper portions of the rivers Itacaiunas, Tapirapé, Paraupebas and Manuel Alves da Natividade, flowing into the Rio Tocantins, Brazil ( Fig. 9 View FIGURE 9 ).

Remarks. The holotype of Rhinopetitia myersi   (MHNH 2229–03) was collected in 1959 and is poorly preserved (see Netto-Ferreira et al., 2014: 1542, Fig. 2 View FIGURE 2 ), so that accurate meristic and morphometric data could not be taken and some of these that appear herein in the species description are those found in Géry’s (1964:454–455) description, some of which are not precise [as for example the number of outer row premaxilary teeth (6 or 7), of anterior dentary teeth (4 or 5), and lateral line scales (31–37). Géry also did not mention the presence of a vertically elongate humeral dark blotch that is quite evident in recently collected specimens.