Genus Acrolebias Costa, 2008 stat. nov.

Acrolebias Costa, 2008 as a subgenus of Austrolebias .

Type species: Cynolebias carvalhoi Myers, 1947 .

Diagnosis: Acrolebias differs from all other genera of the Austrolebias genus group by unique male coloration consisting of golden body flanks with eight to nine purple-grey bars.

Additionally, this genus can be identified by the following unique combination of characters: no contact organs on anal fin in male; bases of pelvic fins separated by small interspace; anal fin short in females; urogenital papillae not attached to anal fin; dorsal fin origin anterior to anal fin origin; 21 or 22 dorsal fin rays in males, 16–18 in females; 21or 22 anal fin rays in males, 16–18 in females; and 27–29 longitudinal series scales (Costa 2006a).

Differential diagnosis: The genus Acrolebias can be distinguished from all other genera of the Austrolebias genus group by having <40 scales in the longitudinal series (vs.> 40 scales in Titanolebias); by the presence of scales in the preopercular region (vs. absent in Gymnolebias); by the basal and medial region of pectoral fins being non-hyaline in adult males (vs. hyaline in Amatolebias, Austrolebias and Garcialebias); by the lack of contact organs on the anal fin of males (vs. present in Acantholebias and Cypholebias); by the rostral region scaled and vertically directed suborbital bar (vs. suborbital bar posteriorly directed and anterior region of head near rostral neuromasts without scales in Megalebias); by markings on the distal portion of the dorsal fin, if present, not fused (vs. present and fused in Argolebias); and by unpaired fins dark grey on males (vs. with bluish to greenish iridescences in Matilebias).

Synapomorphies: We redefine Acrolebias as a monotypic genus that presents the following five morphological autapomorphies (see Supporting Information, Appendix S5): pastel yellow to golden centre of most scales on ventral half of flank, above anal fin, in males (1:2); male pelvic fin bases separated by an interspace (57:0); <14 abdominal vertebrae (169:0); dorsal radial of pectoral fin present (189:1); and flanks with well-defined and regular vertical dark grey bars (16:1).

Included species: Acrolebias carvalhoi (Myers, 1947) comb. nov.

Distribution: Upper Iguazú River basin.