Acantholebias Costa, 2008

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 : 289-290

Genus Acantholebias Costa, 2008 stat. nov.

Acantholebias Costa, 2008 as a subgenus of Austrolebias .

Type species: Cynolebias luteoflammulatus Vaz-Ferreira et al. 1964 .

Diagnosis: Acantholebias is distinguished from all other genera of the Austrolebias genus group by the following unique combination of characters: (1) wide border of most scales on dorsal flank, below dorsal fin and anterior to this fin, excluding the dorsum, in mature dominant males (not considering bands, bars and iridescent lines) light grey to brownish grey, in dominant mature males; (2) absence of iridescent markings on the flank in males; (3) dorsal fin with a dark grey vertical bar on posterior portion in males, more visible in juvenile; (4) background colour of pectoral fins in males bright blue-green; (5) contact organs in the anal fin with bone support in males; and (6) parasphenoid posterior process broadening gradually.

Differential diagnosis: The genus Acantholebias 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 ); the basal and medial region of the pectoral fins non-hyaline in adult males (vs. hyaline in Amatolebias , Austrolebias , Gymnolebias and Garcialebias ); scaled rostral region, vertically directed subocular bar and pelvic fins without an obvious interspace in males (vs. in Megalebias : posteriorly directed subocular bar, anterior region of head near rostral neuromasts without scales and conspicuous interspace between pelvic fins in males); by the lack of a gap between preopercular and mandibular series of neuromasts (vs. gap present in Argolebias , Ga. araucarianus and Acrolebias carvalhoi ); by the lack of iridescent spots on the unpaired fins (vs. present in Acrolebias and Matilebias ); and by the presence of ossified contact organs in the anal fin of males (vs. present but not ossified in Cypholebias ).

Synapomorphies: Acantholebias is supported by 19 molecular synapomorphies and the following six morphological synapomorphies (see Supporting Information, Appendix S5): dorsal fin with a dark grey vertical bar on posterior portion in males (35:1); background colour of pectoral fins in males bright blue-green (42:4); dark grey pigmentation pattern on flank of females: dots (45:0); contact organs on the anal fin in males (86:1); bone support in contact organs in males (87:1); and parasphenoid posterior process gradually broadening (162:0).

Included species: Acantholebias luteoflammulatus (Vaz-Ferreira, Sierra de Soriano & Scaglia de Paulete, 1965) comb. nov. and Acantholebias quirogai ( Loureiro, Duarte & Zarucki 2011) comb. nov.

Distribution: The upper basin of the Negro River (lower Uruguay River), Atlantic basins of eastern Uruguay and basins associated with the Merín lagoon, in Brazil and Uruguay.