Gymnolebias Costa, 2008 as a subgenus of Austrolebias.

Type-species: by original designation as Cynolebias gymnoventris Amato, 1986.

Etymology: naked (from Greek: gymnos) and Lebias, another Cyprinodontiformes genus, in reference to the lack of scales on venter.

Included species: Gymnolebias gymnoventris Amato, 1986 comb. nov. and Gymnolebias jaegari Costa & Cheffe, 2002 comb. nov.

Diagnosis in 2023: Gymnolebias can be distinguished from other Austrolebias genus group genera by the following unique combination of characters: (1) scales absent on ventral region; (2) absence of conspicuous suborbital and supraorbital dark grey marks in living specimens; and (3) flanks dark brownish grey to black, with wide dark grey bars on anterior portion (modified from Costa 2008).

Differential diagnosis:

In addition to the unique combination of character states mentioned in the Diagnosis above, the genus Gymnolebias 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 lack of ossified contact organs in the anal fin of males (vs. present in Acantholebias); by the basal and medial region of the pectoral fins being hyaline in adult males (vs. non-hyaline in Acrolebias, Cypholebias, Matilebias, Argolebias and Megalebias); anal fin rounded in females (vs. nearly triangular in Austrolebias and Garcialebias); and male pectoral fins without black margin (vs. black distal margin in Amatolebias) Synapomorphies: Gymnolebias was recovered as a monophyletic clade supported by 26 molecular characters and the following five morphological characters (see Supporting Information, Appendix S5): wide border of most scales on ventral half of flank, above anal fin, in dominant mature males (not considering bands, bars and iridescent lines) dark grey to black); centre of most scales in mid-dorsal portion of flank, anterior to dorsal fin, in dominant mature

males (not considering bands, bars and iridescent lines) dark grey to black); dark suborbital bar absent (diffused and inconspicuous); scales in the preopercular region absent); and < 14 abdominal vertebrae).

Distribution: Basins associated with the Patos-Merín lagoon system, in Brazil and Uruguay

Literature:

Costa, W.J.E.M. 2008. Catalog of aplocheiloid Killifishes of the World. Universidade Federal do Rio de Janeiro Ed., Rio de Janeiro, Brasil, 55.

Loureiro, Sa, Serra, Alonso, Lanés, Volcan, Calviño, Nielsen, Duarte & Garcia, 2018 : molecular and morpho-combined full revision of Austrolebias, with major reshuffling of components into subgenera, with subgenus Argolebias as primitive to all and a probably distinct bitypic genus, with 6 other subgenera, Acantholebias (valid), Acrolebias (probably valid), Austrolebias s.s. (valid), Gymnolebias (unstable), Cypholebias (unstable), Megalebias (valid), conservatively maintained {without new diagnoses} and 2 un-named subgenera.

Alonso F., G.E. Terán, W.S. Serra Alanís, P. Calviño, M.M. Montes, I.D. Carcía, J.A. Barneche, A. Almirón, L. Ciotek, P. Giorgis, J. Casciotta, 2023. From the mud to the tree: phylogeny of Austrolebias killifishes, new generic structure and description of a new species (Cyprinodontiformes: Rivulidae) Zool. Journ. of the Linnean Society, XX, 1-30, Fig. 15, Tab. 2.

See: Austrolebias group introduction page for comment.