Astyanax microschemos, Bertaco & de Lucena, 2006

Bertaco, Vinicius A. & de Lucena, Carlos A. S., 2006, Two new species of Astyanax (Ostariophysi: Characiformes: Characidae) from eastern Brazil, with a synopsis of the Astyanax scabripinnis species complex, Neotropical Ichthyology 4 (1), pp. 53-60 : 54-56

Astyanax microschemos , new species

Figs. 1-3 , Table 1

Holotype. MCP 37569 (55.1 mm SL), córrego Palmital , rio Itapemirim drainage, Iúna, Espírito Santo, Brazil, approx. 20º21’S 41º31’W, 14 Jan 2003, R. L. Teixeira & G. I. Almeida.

Paratypes. MCP 34366, 31 (3 c&s), 35.2-55.1 mm SL, collected with the holotype .

Diagnosis. Astyanax microschemos belongs to the A. scabripinnis species complex and differs from species outside this complex by the lower number of branched anal-fin rays (14-18 vs 20-45) and the shallow body depth (26.9-29.7 vs more than 35% of SL). The combination of the shallow body depth (26.9-29.7% of SL), and the smaller interorbital width (26.9-30.4% of HL), versus the deeper body depth (29.7-35.6% of SL) and greater interorbital width (29.4-38.8% of HL), distinguish it from remaining species of the complex.

Description. Morphometric data summarized in Table 1 . Body compressed and elongate; greatest body depth usually located anterior to dorsal-fin origin. Dorsal profile of head between vertical through posterior nostril and tip of supraoccipital spine straight or slightly convex. Profile of body convex from tip of supraocciptal spine to base of last dorsal-fin ray, and straight from that point to adipose-fin origin. Ventral profile of body slightly convex from vertical through posterior nostril to pectoral-fin insertion, and nearly straight from that point to anal-fin origin. Body profile along anal-fin base posterodorsally slanted. Caudal peduncle elongate and nearly straight to slightly concave along both dorsal and ventral margins.

Snout profile rounded from margin of upper lip to vertical through anterior nostrils. Head small. Mouth terminal, lower jaw slightly longer than upper jaw. Maxilla extending posteri- orly to vertical through anterior margin of orbit, slightly curved, and aligned at angle of approximately 45 degrees relative to longitudinal body axis. Anterodorsal border of maxilla concave, posterodorsal border slightly convex, and ventral bor- der convex. Maxilla slightly widened anteroposteriorly.

Premaxilla with two tooth rows; outer row with three pentacuspid teeth with central cusp longer. Five teeth in inner premaxillary row; teeth gradually decreasing in length from first towards fourth teeth with last tooth distinctly smaller: teeth with five to seven cusps with central cusp twice as long and broad as other cusps. Maxilla with two or three (usually two) teeth with tree to five cusps and central cusp longest. Four anterior-most dentary teeth larger, with five or seven cusps, followed by one medium-sized tooth with five cusps, and then four or five teeth with one to three cusps. Central cusp in all teeth two to three times as long and broad as other cusps. All cusp tips slightly curved posteriorly towards inside of mouth ( Fig. 3 ).

Dorsal-fin rays ii, 9 (n = 20); first unbranched ray approximately one-half length of second ray. Distal margin of dorsalfin nearly straight or slightly convex. Dorsal-fin origin approximately at middle of SL.Adipose-fin located approximately at vertical through insertion of base of last anal-fin ray. Analfin rays iv-v, 15-17 (rarely 14 or 18, mean = 16.1, n = 20). First unbranched ray normally only apparent in cleared and stained specimens. Distal border of anal fin smoothly concave. Analfin origin situated posterior to vertical through base of last dorsal-fin ray. Pectoral-fin rays i, 11-13 (mean = 11.9, n = 20). Tip of pectoral fin falls one or two scales short of vertical through pelvic-fin insertion. Pelvic-fin rays i, 7 (n = 20). Pelvic-fin origin located slightly anterior to vertical through dorsal-fin origin. Tip of pelvic fin reaching posterior portion of genital open, but falling short of anal-fin origin.

Caudal-fin forked with lobes of similar size and 19 principal rays. Dorsal procurrent rays 9-11. Ventral procurrent rays 9-10 (n = 3).

Scales cycloid, moderately large. Lateral line complete. Scales in lateral line series 36-38 (mean = 37, n = 20). Scale rows between dorsal-fin origin and lateral line 5-6 (mean = 5.2, n = 20); 4-5 scale rows between lateral line and pelvic-fin origin (mean = 4.2, n = 20). Predorsal scales 10-12 (mean = 10.7, n = 20) arranged in regular series. Scale rows around caudal peduncle 14 (n = 20). Scale sheath along anal-fin base formed by 4-8 scales in single series covering base of anterior-most rays.

Precaudal vertebrae 17-18; caudal vertebrae 18-19; total vertebrae 35-36. Supraneurals 5-6. Gill-rakers 6/10 (n = 3).

Color in alcohol. Dorsal and dorsolateral portions of head and body dark brown. Dark chromatophores scattered on lateral portion of head, but more densely concentrated on snout and anterior border of eye. Dorsal portion of body densely pigmented in larger specimens. Scales on midlateral surface of body bordered with dark brown chromatophores forming reticulate pattern. Body with black, pigmented, midlateral stripe extending from humeral region to base of middle caudal-fin; faint dark pigmentation present of middle caudal-fin rays. Midlateral body stripe expanded dorsally and ventrally proximate to caudal-fin base and forming small caudal spot. Single black, narrow, vertically-elongate humeral spot present with dorsal portion of spot wider. Spot located over second to fourth lateral-line scales and extending over 2 or 3 horizontal series of scales, including lateral line. Fins with scattered dark chromatophores ( Fig. 2 ).

Sexual dimorphism. Secondary sexual characters were not found on examined specimens.

Distribution. Astyanax microschemos is known only from the upper-most headwaters of the rio Itapemirim drainage, a coastal drainage in Espírito Santo State of eastern Brazil ( Fig. 1 ).

Etymology. The species name is from the Greek, mikroschemos, low stature, referring to the shallow body depth of the species.

Ecological notes. At the type-locality the córrego Palmital is about 2 m wide, with clear water, segments with rapids, riparian vegetation, and a substrate of stones and rocks. Astyanax microschemos was collected with Characidium sp., Neoplecostomus sp. and Trichomycterus sp.

Figures

Fig. 1. Coastal drainages of states of Espírito Santo and Bahia, eastern Brazil, showing the distribution of Astyanax microschemos (dot) and Astyanax pelecus (square).

Fig. 2. Astyanax microschemos, MCP 37569, holotype, 55.1 mm SL; córrego Palmital, rio Itapemirim drainage, Iúna, Espírito Santo, Brazil.

Fig. 3. Astyanax microschemos, MCP 34366, paratype, 46.3 mm SL. SEM image of left side upper and lower jaws teeth.