History:

1876: Steindachner F. describes the genus Cynolebias. Type-species: by monotypy as Cynolebias porosus Steindachner, 1876.

1998; Costa W. splits Cynolebias into 3 genera i.e., Cynolebias, Austrolebias. (Type-species: by original designation as Cynolebias bellottii Steindachner, 1881.) and Megalebias (Type-species: by original designation as Cynolebias wolterstorffi Ahl, 1924).

2006: Costa W., synonimizes Megalebias with Austrolebias.

2008: Costa W., erects 6 new subgenera in Austrolebias i.e., Acantholebias, (Type-species: by original designation (also monotypic) as Cynolebias luteoflammulatus Vaz-Ferreira, Sierra & Paulette, 1964.); Acrolebias, (Type-species: by original designation as Cynolebias carvalhoi Myers,1947.); Austrolebias, Type-species: by original designation as Cynolebias bellottii Steindachner, 1881.); Argolebias, (Type-species: by original designation as Cynolebias nigripinnis Regan, 1912.); Cypholebias, (Type-species: by original designation as Cynolebias robustus Günther, 1883.); Gymnolebias, (Type-species: by original designation as Cynolebias gymnoventris Amato, 1986); and redifines the former Megalebias as the 7th subgenus in Austrolebias. (Type-species: by original designation as Cynolebias wolterstorffi Ahl, 1924).

2018: Lanes et al. came with a molecular and morpho-combined full revision of Austrolebias, with major reshuffling, and proposed 2 unnamed subgenra to be added to the already 7 excisting subgenera, but without proper diagnoses.

2023: On July 10, 2023, the paper by Alonso et al., a group scientists from Argentina and Uruguay, was published, in which they rearranged the classification of the genus Austrolebias. Alonso et. al., up-levels all 7 sub genera into genus status, changes the position of several species in the existing sub genera and add 4 new genera to the then 7 genera making 11 genera in total. His team makes work from the diagnoses and provide a key to make the basic differences between the new genera clear. They explain this move as being possible subjective, but give their reasons to to so. Also, they described in this very complete work a new species named "guarani," which they classified in the new erected genus Argolebias. The other genera are: Acantholebias; Acrolebias; Amatolebias; Austrolebias; Carcialebias; Cypholebias; Gymolebias; Matilebias; Megalebias and Titanolebias.

Genus Acantholebias Costa, 2008 stat. nov.

Type-species: by original designation as Cynolebias luteoflammulatus Vaz-Ferreira, Sierra & Paulette, 1964.)

Included species:

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

Diagnosis:

Acantholebias is distinguished from all other genera of the Austrolebias 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 pectoralfins 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; background colour of pectoral fins in males bright blue-green; dark grey pigmentation pattern on flank of females: dots; contact organs on the anal fin in males; bone support in contact organs in males; and parasphenoid posterior process gradually broadening.

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.

Literature:

Steindachner, F. 1876. Ichthyologische Beiträge (V). Sitz. Akad. Wiss. Wien mathem.-naturwiss. Klasse Abt.1, 74: 172.

Costa, W.J.E.M. 1998. Phylogeny and Classification of Rivulidae revisited: Origin and Evolution of Annualism and Miniaturization in Rivulid Fishes (Cyprinodontiformes: Aplocheilidei). J. Comp. Biol., 3 (1), December: 75.

Costa, W.J.E.M. 2008. Catalog of aplocheiloid Killifishes of the World. Universidade Federal do Rio de Janeiro Ed., Rio de Janeiro, Brasil, 51.

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 bi-typic genus, with 6 other subgenera, Acantholebias (valid), Acrolebias, Austrolebias s.s., Gymnolebias, Cypholebias, Megalebias , 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 comments.