Megalebias Costa, 1998

Alonso, Felipe, Terán, Guillermo Enrique, Alanís, Wilson Sebastián Serra, Calviño, Pablo, Montes, Martin Miguel, García, Ignacio Daniel, Barneche, Jorge Adrián, Almirón, Adriana, Ciotek, Liliana, Giorgis, Pablo & Cascioưa, Jorge, 2023, From the mud to the tree: phylogeny of Austrolebias killifishes, new generic structure and description of a new species (Cyprinodontiformes: Rivulidae), Zoological Journal of the Linnean Society 199 (1), pp. 280-309 : 290

Genus Megalebias Costa, 1998

Megalebias Costa, 1998 as genus. Synonym of Austrolebias but valid as a subgenus by Costa (2006a).

Type species: Cynolebias wolterstorffi Ahl, 1924 (type by original designation).

Diagnosis: The genus Megalebias can be differentiated from all other genera of the Austrolebias genus group by the following unique combination of character states: (1) absence of scales in the anterior portion adjacent to the rostral neuromasts; (2) contact organs on upper pectoral fin rays of males; (3) lack of contact organs on the anal fin; (4) 35–40 lateral line scales; and (5) pelvic fin bases separated by a gap in males.

Differential diagnosis: The genus Megalebias 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 non-hyaline in adult males (vs. hyaline in Amatolebias , Austrolebias and Garcialebias ); by the lack of contact organs in the anal fin of males (vs. present in Acantholebias and Cypholebias ); by the absence of vertical bars on the flanks of the males (vs. present in Acrolebias ); and by the posteriorly directed subocular bar, anterior region of head near rostral neuromasts without scales and conspicuous interspace between pelvic fins in males (vs. vertically to anteriorly directed bar, anterior region of head scaled and interspace between pelvic fins in males small or absent in Argolebias and Matilebias ).

It presents 133 genetic autapomorphies and the following morphologicalautapomorphies (seeSupportingInformation,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 (3:0); centre of most scales on dorsal half of flank, anterior to dorsal fin, in dominant mature males (not considering bands, bars and iridescent lines) dark grey to black (11:1); and male pelvic fin bases separated by an interspace (57:0).

Included species: Megalebias wolterstorffi (Ahl, 1924) .

Distribution: Plains and wetlands of the Patos-Merín lagoon system in Uruguay and Brazil.