Astyanax gymnodontus

description

Description. Body elongated and laterally compressed, body deeper at dorsal-fin origin. Predorsal and prepelvic regions of body rounded transversely. Dorsal profile of snout convex, straight or slightly concave from eye to supraoccipital process. Dorsal profile of body gently convex from supraoccipital process to dorsal-fin end, straight or slightly convex from this point to adipose-fin base, straight or slightly concave from this point to caudal fin. Ventral profile of body convex, between anterior tip of jaw and pelvic-fin origin, straight from this point to anal-fin origin. Dorsal-fin origin slightly forward or at vertical through pelvic-fin origin, its distal margin straight. Pectoral-fin origin at vertical through posterior edge of opercle, its margin rounded, when adpressed, reaching or almost reaching pelvic-fin origin. Pelvic-fin origin at about vertical through dorsal-fin origin, its margin slightly convex, when adpressed not reaching anal-fin origin. Anal-fin origin just behind vertical through end of dorsal-fin base, its distal margin slightly concave. Caudal fin with symmetric lobes, or inferior slightly longer, and scales only at base. Dorsal-fin rays ii or iii, 8 to 1

A redescription of Astyanax gymnodontus (Eigenmann, 1911), new combination, a polymorphic characid fish from the rio Iguaçu basin, Brazil

diagnosis

Diagnosis. Astyanax gymnodontus can be distinguished from all other congeners at the rio Iguaçu basin except for A. varzeae by the combination of the following characters: thirdinfraorbital margin separated from preopercle by broad skin area as wide as 1 / 5 to 1 / 3 of its depth (vs. adjacent or separated by a narrower skin area); teeth with a cutting edge forming a straight line or a convex arc in frontal view (vs. concave arc); premaxillary teeth with five (rarely seven) cusps, with the median being the largest and the other cusps abruptly decreasing in size to the sides (vs. commonly seven, rarely four, five or nine cusps, gradually decreasing laterally); transversally located black humeral blotch (vs. longitudinally located); 21 to 24 anal-fin rays and 37 to 41 lateral-line scales (vs. 18 to 22 and 34 to 38, respectively, in A. totae); and no hooks on pelvic or anal fins. Astyanax varzeae is the congener most similar to A. gymnodontus in the basin, but the latter can be diagnosed by having a deeper body, 2.4 to 3 times in the SL (vs. 3 or 3.5 in A. varzeae), and a longer snout, 3.2 to 4.7 times in the HL (vs. 4.3 to 6.1).

A redescription of Astyanax gymnodontus (Eigenmann, 1911), new combination, a polymorphic characid fish from the rio Iguaçu basin, Brazil

distribution

Distribution. Astyanax gymnodontus is only known to occur in the rio Iguaçu basin in Southern Brazil (Fig. 6).

A redescription of Astyanax gymnodontus (Eigenmann, 1911), new combination, a polymorphic characid fish from the rio Iguaçu basin, Brazil

materials_examined

type-locality: Porto União, rio Iguaçu; illustration; holotype FMNH 54574, ex CM 3204).

A redescription of Astyanax gymnodontus (Eigenmann, 1911), new combination, a polymorphic characid fish from the rio Iguaçu basin, Brazil