Hemibrycon tridens Eigenmann, 1922

Bertaco, Vinicius A. & Malabarba, Luiz R., 2010, A review of the Cis-Andean species of Hemibrycon Günther (Teleostei: Characiformes: Characidae: Stevardiinae), with description of two new species, Neotropical Ichthyology 8 (4), pp. 737-737: 737-

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http://doi.org/ 10.1590/S1679-62252010000400005

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Hemibrycon tridens Eigenmann, 1922
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Hemibrycon tridens Eigenmann, 1922  

Fig. 25 View Fig

Hemibrycon tridens Eigenmann, 1922: 152   (species described in key, distribution: extralimital, río Apurimac at Uruhuasi [ Curuhuasi , upper río Ucayali drainage, Peru]). - Eigenmann, 1927: 402 (in key), 403-404 (pl. 96, fig. 3, original description, distribution: Uruhuasi, southeastern Peru; holotype 13723 IU).

Diagnosis. Hemibrycon tridens   is readily distinguished from all congeners, except H. beni   , by the number of branched anal-fin rays (17 vs. 18-34, Fig. 2 View Fig ). Hemibrycon tridens   differs from H. beni   by the number of lateral line scales (39 vs. 44- 53, Fig. 3), and by the number of scale rows above and below lateral line (6 and 5 vs. 7-8 and 6-8, respectively). Among remaining Cis-Andean species of Hemibrycon   , only H. helleri   and H. mikrostiktos   have lower branched anal-fin rays (19-23 and 18-21). From these species, H. tridens   differs additionally by the number of lateral line scales (39 vs. 40-42 and 42-45, respectively).

Description. Morphometric data for H. tridens   summarized in Table 5. Largest male 51.5 mm SL. Body compressed and elongate; greatest body depth anterior to dorsal-fin origin. Dorsal profile of head convex. Dorsal body profile convex from occipital bone to base of last dorsal-fin ray; straight from this point to adipose-fin origin. Ventral profile of head slightly convex. Ventral body profile convex from pectoral-fin origin to pelvic-fin origin, and straight to slightly convex to anal-fin origin. Body profile along anal-fin base posterodorsally slanted. Caudal peduncle elongate, nearly straight to slightly concave along dorsal and ventral margins.

Snout rounded from margin of upper lip to vertical through anterior nostrils. Head relatively small. Mouth sub-terminal, mouth slit nearly at horizontal through inferior margin of eye. Maxillalongandslightlycurved, alignedatangleofapproximately 45º to longitudinal body axis, and its posterior tip extending below orbit, reaching nearly to vertical through center of eye.

Premaxilla with two tooth rows; outer row with 5 tricuspid teeth with central cusp slightly longer; inner row with 4 tri- to pentacuspids teeth, gradually decreasing in length from first to third teeth and last tooth smallest; central cusp twice or three times longer and broader than other cusps. Maxilla fully toothed with 12 tricuspid teeth, with central cusp longer. Three anteriormost dentary teeth larger, with 5 cusps, followed by medium sized tooth with 3 cusps, and 8 teeth with 1-3 cusps or conical; central cusp in all teeth two to three times longer and broader than other cusps. Cusp tips slightly curved posteriorly and lingually.

766 A review of the Cis-Andean species of Hemibrycon  

Dorsal-fin rays ii,8, first unbranched ray approximately onehalf length of second ray. Dorsal-fin origin located posterior to middle of SL and posterior to vertical through pelvic-fin origin. Profile of distal margin of dorsal fin slightly concave. Dorsal fin without bony hooks. Adipose-fin located at vertical through insertion posterior to last anal-fin ray.Anal-fin rays iii,17 ( Fig. 2 View Fig ). Anal-fin profile slightly nearly straight. Anal-fin origin approximately at vertical through insertion in the last dorsal fin rays.Anal-fin rays of male bearing one pair of small bony hooks along posterolateral border of each segment of lepidotrichia, along last unbranched ray and sixteenth branched rays. Hooks located along anteriormost branch and proximal 1 /2 to 2 /3 of each ray. Pectoral-fin rays i,10. Pectoral-fin tip surpassing pelvicfin origin. Pectoral fin without bony hooks. Pelvic-fin rays i,6,i. Pelvic-fin tip nearly reaching anal-fin origin. Pelvic-fin origin located 4 predorsal scales anterior to vertical through dorsalfin origin. Pelvic fin of male bearing one small bony hook per segment of lepidotrichia along ventromedial border of second to seventh branched rays. Caudal fin forked with 19 principal rays without bony hooks; lobes similar in size. Caudal-fin base with a few scales. Dorsal procurrent rays 10 and ventral procurrent rays 10 (holotype x-ray).

Scales cycloid, moderately large. Lateral line complete with 39 ( Fig. 3). Scale rows between dorsal-fin origin and lateral line 6; scale rows between lateral line and pelvic-fin origin 5. Predorsal scales 14, arranged in regular series. Scales rows around caudal peduncle 14.

Precaudal vertebrae 18; caudal vertebrae 22; total vertebrae 40. Supraneurals 5 (holotype x-ray). Gill rakers on upper limb of outer gill arch 5, on lower limb 10.

Color in alcohol. Holotype badly preserved. Humeral and caudal peduncle spot not evident. Base of caudal fin and middle rays black pigmented. Distal half of dorsal fin with dark pigmentation, and caudal and anal fin with dark brown pigmentation diffuse. Pectoral and pelvic fins hyaline. Body yellowish. Left side of holotype has three black marks due to preservation artifacts ( Fig. 25 View Fig ). Eigenmann (1927: 404) described the color pattern “A dark lateral band, caudal spot, and middle caudal rays dusky; distal parts of dorsal and anal and outer part of caudal lobes dusky; margin of lower caudal lobe dusky”.

Sexual dimorphism. Male of Hemibrycon tridens   is easily recognized by the presence of bony hooks on the anal- and pelvic-fin rays. No gill gland was observed on first gill arch.

Distribution. Hemibrycon tridens   is known from río Apurimac, upper río Ucayali drainage, Curuhuasi, Peru ( Fig. 4 View Fig ).

Remarks. Eigenmann (1922: 152) proposed Hemibrycon tridens   based on one specimen, diagnosed in his key to Hemibrycon species.   Only in 1927, Eigenmann presented a full description, and designated IUM 13723 View Materials (now CAS 44358 View Materials ) as the type specimen. The holotype is the only known specimen. The type locality provided by Eigenmann (1922) for H. tridens   was “Rio Apurimac at Uruhuasi”. According to Hernán Ortega (pers. comm.), the correct type locality of H. tridens   is the río Apurimac at Curuhuasi, upper río Ucayali drainage. He believed that Eigenmann erroneously wrote “Uruhuasi” instead of Curuhuasi.

Material examined. Holotype. CAS 44358 View Materials , male (x-ray), 51.5 mm SL, Peru, 24 leagues from Cusco, Curuhuasi, province of Aymaraes, Department of Apurimac, F. Rosenberg.  

CAS

California Academy of Sciences