Hemibrycon mikrostiktos, Bertaco & Malabarba, 2010

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 : 754-756

Hemibrycon mikrostiktos , new species

Figs. 16-17

Holotype. MUSM 35490 , 44.4 mm SL, río Aguaytía , río Negro , upper río Ucayali basin, Aguaytía, Padre Abad, Ucayali, Peru, 09º02’34”S 75º30’45”W, 2 Nov 1999, P. de Rham & F. Chang.

Paratypes. MCP 44521, 10 (3 c&s), 27.6-42.4 mm SL; MUSM 15845, 19 measured and counted of 187, 24.5-42.4 mm SL; UFRGS 12003, 10 , 30.9 -36.0 mm SL, collected with the holotype .

Diagnosis. Hemibrycon mikrostiktos is readily distinguished from all congeners by the size of the humeral spot (2-3 vs. 4-9 horizontal series of scales), number of scale rows below of the lateral line (3-4 vs. 4-8), and total number of pelvic-fin rays (7 vs. 8). Furthermore, H. mikrostiktos differs from most congeners by the number of branched anal-fin rays (18-21 vs. 21-34, and 17 in H. tridens , Fig. 2 ), except H. beni and H. helleri . It differs from H. beni and H. helleri by the number of lateral line scales (40-42 vs. 44-53 and 42-44, Fig. 3).

Description. Morphometric data for Hemibrycon mikrostiktos summarized in Table 4. Largest specimen 44.4 mm SL. Body compressed and moderately elongate; greatest body depth at vertical through middle length of pectoral fins. Dorsal profile of head nearly straight. Dorsal body profile convex from occipital bony to dorsal-fin origin; posteroventrally slanted at dorsal-fin base; straight from last dorsal-fin ray to adiposefin 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 analfin base posterodorsally slanted. Caudal peduncle short, 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 terminal, mouth slit nearly at horizontal through below middle of eye. Maxilla long and slightly curved, aligned at angle of approximately 45 o 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 4-6, 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 toothed with 7-11 tri- to pentacuspid teeth, except for last three or four conical teeth, with central cusp longer. Three anteriormost dentary teeth larger, with 5 cusps, followed by medium sized tooth with 3 cusps, and 12-13 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 ( Fig. 17 ).

Dorsal-fin rays ii,8 (n = 20); 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. First dorsal-fin pterygiophore

V. A. Bertaco & L. R. Malabarba 755

inserted between the neural spines of eleventh to twelfth vertebrae (n = 3). Profile of distal margin of dorsal fin convex. Adipose-fin located at vertical through insertion of last or posterior to last anal-fin ray. Anal-fin rays iii-iv,18-20 (two with 21, mode = 19, n = 20, Fig. 2 ). Anal-fin profile slightly concave in all specimens. First anal-fin pterygiophore inserted between the haemal spine of last precaudal vertebra and the first caudal vertebrae.Anal-fin origin approximately at vertical through insertion in the middle dorsal fin. Pectoral-fin rays i,9-10 (mode = 9, n = 20). Pectoral-fin tip reaching pelvic-fin origin. Pelvic-fin rays i,5,i (n = 15) or i,6 (n = 5). Pelvic-fin origin located 3-4 predorsal scales anterior to vertical through dorsal-fin origin. Caudal fin forked with 19 principal rays (n = 20); lobes similar in size. Basal portion of caudal-fin lobes covered with irregular scales and smaller than those of the body, following by one larger scale in each lobe. Dorsal procurrent rays 12-13 and ventral procurrent rays 12-14 (n = 3).

Scales cycloid, moderately large. Lateral line complete with 40-42 (mode = 41, n = 16, Fig. 3).[Scale rows between dorsalfin origin and lateral line 6-7 (mode = 6, n = 18); scale rows between lateral line and pelvic-fin origin 3-4 (mode = 4, n = 18). Predorsal scales 14, arranged in regular series (n = 18). Scales rows around caudal peduncle 14 (n = 18). Axillary scale on pelvic-fin origin extends posteriorly covering 2-3 scales. Scale sheath along anal-fin base with 7-10 scales in single series, extending to base of most anterior branched rays.

Precaudal vertebrae 17; caudal vertebrae 23-24; total vertebrae 40-41. Supraneurals 6-7 (n = 3). Gill rakers on upper limb of outer gill arch 5-6, and on lower limb 9-10 (n = 5).

Color in alcohol. Dorsal portion of head and body with dense concentration of black chromatophores. Dorsal and dorsolateral portion of caudal peduncle near caudal fin base densely pigmented. Dorsolateral portion of body with scattered black chromatophores. Snout and upper portion of maxilla densely pigmented. Infraorbitals and opercle with scattered black chromatophores. Midlateral body silvery and dark pigmented. One small black humeral spot, located over third to fourth lateral line scales and extending over 1-2 horizontal series of scales, sometimes including lateral line. Base of caudal fin and middle rays black pigmented. Abdominal region almost devoid of black chromatophores. Dorsal, adipose, anal and caudal fin with dark pigmentation diffuse. Pectoral and pelvic fins hyaline ( Fig. 16 ).

Sexual dimorphism. None of the type specimens examined had hooks on fins or any other apparent sexually dimorphic features. Gill glands were not found on first gill arch.

Distribution. Hemibrycon mikrostiktos is known from río Aguaytía, upper río Ucayali drainage, Ucayali, Peru ( Fig. 4 ).

756 A review of the Cis-Andean species of Hemibrycon

Etymology. The name mikrostiktos is from the Greek, mickros, small, and stiktos, spot, referring to the small humeral spot. A noun in apposition.

Figures

Fig. 16. Hemibrycon mikrostiktos, MUSM 35490, holotype, 44.4 mm SL, upper río Ucayali basin, Peru.

Fig. 17. Hemibrycon mikrostiktos, MCP 44521, paratype, female, 35.7 mm SL. Scanning electron micrograph of left side upper and lower jaws. Scale bar = 1 mm.

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.