Hemibrycon beni Pearson, 1924

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. 737-770 : 739-741

Hemibrycon beni Pearson, 1924

Fig. 1

Hemibrycon beni Pearson, 1924: 42-43 (original description; type material; type locality: Espia and río Colorado, lower Bopi, Bolivia), 62-63 (pl. 2, fig. 6, cotype).

Diagnosis. Hemibrycon beni is readily distinguished from most congeners, except H. mikrostiktos , H. paez , H. tridens , and H. virolinica , by the number of branched anal-fin rays (15-19 vs. 20-34, Fig. 2 ). Hemibrycon beni differs from these species by the number of lateral line scales (44-53 vs. 40-42, 39-42, 39, and 40-44, respectively). Furthermore, H. beni differs from H. virolinica by the number of predorsal scales (17-20 vs. 10-15). The branched anal-fin ray counts of H. beni overlapping somewhat the H. helleri counts (15-19 vs. 19-23), but they can be distinguished further by the size of humeral spot (3-4 vs. 7-8 horizontal series of scales), and by total number of vertebrae (38-39 vs. 41-43).

Description. Morphometric data for H. beni summarized in Table 1. Largest male 81.4 mm SL, largest female 34.3 mm SL. Body compressed and moderately elongate; greatest body depth usually at vertical through middle length of pectoral fins. Dorsal profile of head straight to slightly convex. Dorsal body profile convex from occipital bone to base of last dorsalfin ray; straight from this point to adipose-fin origin. Ventral profile of head 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 small. Mouth terminal, mouth slit nearly at horizontal through below middle of eye. Maxilla long and slightly curved, aligned at angle of approximately 45º to longitudinal body axis, and its posterior tip extending below orbit, reaching nearly to vertical through center of eye.

Premaxilla with two teeth rows; outer row with 4-5 tricuspid teeth with central cusp slightly longer; inner row with 4 pentacuspid 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 7-14 uni- to tricuspid teeth, with central cusp longer. Three anteriormost dentary teeth larger, with 3-5 cusps, followed by medium sized tooth with 3 cusps, and 8-9 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.

Dorsal-fin rays ii,8 (one with ii,7 and one with iii,8; n = 30); first unbranched ray approximately one-half 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 convex. Dorsal fin without bony hooks. Adipose-fin located at vertical through insertion of last or posterior to last anal-fin ray. Anal-fin rays iii-iv,16-18 (one with 15 and two with 19, mode = 17, n = 35, Fig. 2 ). Anal-fin profile slightly convex in males and nearly straight in females. Anal-fin origin approximately at vertical through insertion in the last dorsal fin rays. Anal-fin rays of males bearing one pair of small bony hooks along posterolateral border of each segment of lepidotrichia, usually along last unbranched ray and third to fourth branched rays. Hooks usually located along posteriormost branch and distal 1 / 2 to 2 / 3 of each ray. Pectoral-fin rays i,10-11 (mode = 10, n = 33). Pectoral-fin tip reaching pelvic-fin origin in all specimens. Pectoral fin without bony hooks. Pelvic-fin rays i,6,i (one with i,5,i, n = 33). Pelvicfin origin located 5-6 predorsal scales anterior to vertical through dorsal-fin origin. Pelvic fin of males usually bearing one small bony hook per segment of lepidotrichia along ventromedial border of second to eighth branched rays. Caudal fin forked with 19 principal rays without bony hooks 740 A review of the Cis-Andean species of Hemibrycon

(n = 33); lobes similar in size. Caudal-fin base with a few scales in half-length, followed by one large scale in each lobe. Caudal fin without bony hooks. Dorsal procurrent rays 10-11 and ventral procurrent rays 11 (n = 2, x-ray).

Scales cycloid, moderately large. Lateral line complete with 44-53 (mode = 45, n = 32, Fig. 3). Scale rows between dorsalfin origin and lateral line 7-8 (mode = 8, n = 33); scale rows between lateral line and pelvic-fin origin 6-8 (mode = 7, n = 33). Predorsal scales17-20, arranged in regular series (mode = 18, n = 33). Scales rows around caudal peduncle 16-18 (mode = 16, n = 32).Axillary scale on pelvic-fin origin extends posteriorly covering two scales. Scale sheath along anal-fin base with 5-8 scales in single series, extending to base of most anterior branched rays.

Precaudal vertebrae 18-19; caudal vertebrae 20; total vertebrae38-39 (n = 3). Supraneurals 7 (n = 1, x-ray).Gill rakers on upper limb of outer gill arch 6, and on lower limb 10-11 (n = 4).

Color in alcohol. Dorsal portion of head and body dark brown. Dorsolateral portion of body with scattered black chromatophores. Midlateral body silvery. One small and vertical black humeral spot, located over third to fourth lateral line scales and extending over 1-2 horizontal series of scales including lateral line, and sometimes over the first horizontal series below lateral line. Base of caudal fin and middle rays black pigmented. Abdominal region almost devoid of black chromatophores. Dorsal, adipose, and caudal fin with dark brown pigmentation diffuse and anal fin with small black chromatophores along its border forming narrow stripe. Caudal peduncle without spot. Pectoral and pelvic fins hyaline ( Fig. 1 ). Body yellowish.

Sexual dimorphism. Males of Hemibrycon beni are easily recognized by the presence of bony hooks on the anal- and pelvic-fin rays. Males and females also slightly differ in body

V. A. Bertaco & L. R. Malabarba 741

depth ( Table 1), and in anal-fin shape, which is slightly convex in males and nearly straight in females. Gill glands were not found on first gill arch in either males or females.

Distribution. Hemibrycon beni is known from río Beni drainage, upper río Madeira basin, where ríos La Paz and Miguilla join to form río Bopi, Espia, La Paz, Bolivia ( Fig. 4 ).

Remarks. Hemibrycon beni was described by Nathan Pearson based on specimens collected by the Mulford Expedition, Bolivia, in 1921. In the original description, Pearson designated 48 “cotypes” in good condition plus 58 “dried during shipment”, all specimens catalogued under IU 17321, and further listed six specimens not identified as types (IU 17347, now CAS 44335). Of the original 106 cotypes under IU 17321, however, there are 107 presently catalogued as cotypes under CAS 44333, 29 specimens, CAS 44334, 60 specimens, USNM 117543, 2 specimens, and UMMZ 66504, 16 specimens. This last lot was not examined. All specimens of the lot CAS 44334 are very dry but the remaining syntypes are in good condition.

Material examined. Syntypes. CAS 44333, 29 (1 x-ray), 24.1- 56.0 mm SL , CAS 44334, 60 , 27.4-81.4 mm SL , USNM 117543 , 2 (x-ray), 31.6-42.1 mm SL, where ríos La Paz and Miguilla join to form río Bopi, río Beni drainage, elev. 3,080 ft., Espia, La Paz, Bolivia, ca. 16º16’S 67º12’W, Jul 1921 , N. E. Pearson. Non -type specimens. CAS 44335, 6 , 22.5-24.8 mm SL, río Colorado , tributary to lower río Bopi 10 mi above Huachi, Mulford Exploration of the Amazon Basin, La Paz, Bolivia, ca. 16º05’S 67º12’W, Sep 1921 .

Figures

Fig. 1. Hemibrycon beni, CAS 44333, syntype, male, 56.0 mm SL, upper río Beni basin, Bolivia.

Fig. 2. Tukey box plots of number of branched anal-fin rays in Hemibrycon species. Mean represented by thick vertical bar, and 25th and 75th percetiles as lateral borders of box plots. Number in parentheses = N.

Fig. 4. Map of central and northern South America showing geographic distribution of Hemibrycon beni (1, solid hexagon), H. divisorensis (2, open triangle), H. helleri (3, ellipse), H. huambonicus (4, solid triangles), H. jelskii (5, solid dots), H. inambari (6, rectangles), H. metae (7, solid squares), H. mikrostiktos (8, open square), H. polyodon (9, inverted triangle), H. surinamensis (10, solid diamonds), H. taeniurus (11,Trinidad Island), H.tridens (12, open circle).Some symbols represent more than one lot or locality of specimens. 1-12 = type locality of each species.