Type species: Cynolebias elongatus Steindachner, 1881..

Included species: Titanolebias calvinoi, Alonso F., Terón G.E., Serra Alanis W.S., Waldbillig M.M., Montes M.M., Bugeau B., Barneche B.A., Shimabukuru M.I., Táboas F.G., Maroli M., Almeida M.J., 2025., Titanolebias cheradophilus (Vaz-Ferreira, Sierra de Soriano & Scaglia de Paulete, 1965) comb. nov., Titanolebias prognathus (Amato, 1986) comb. nov., Titanolebias monstrosus (Huber, 1995) comb. nov. and Titanolebias elongatus (Steindachner, 1881) comb. nov..

Diagnosis:

The new genus Titanolebias differs from all other genera of the Austrolebias genus group by the following unique combination of characters: (1) contact organs on most pectoral fin rays, in males; (2) > 40 scales on the lateral line; (3) small size of scales; (4) centre of most scales on ventral half of flank, above anal fin, in dominant mature males (not considering bands, bars and iridescent lines) pastel yellow to golden; (5) contact organs on the anal fin of males; and (6) absence of scales in the anterior portion adjacent to the rostral neuromasts.

Differential diagnosis:

In addition to the unique combination of character states mentioned in the Diagnosis above, the genus Titanolebias can be distinguished from all other genera of the Austrolebias genus group by having a posteriorly directed suborbital bar and the anterior region of the head, near the rostral neuromasts, without scales (vs. directed vertically, anteriorly or absent and the anterior region of the head, near rostral neuromasts, scaled in Argolebias, Matilebias, Gymnolebias, Acantholebias, Cypholebias, Acrolebias, Garcialebias, Austrolebias and Amatolebias); and by the presence of contact organs in the anal fin of males (vs. contact organs absent in Megalebias). Synapomorphies: The new genus Titanolebias was supported by 30 molecular character states and the following seven morphological character states (see Supporting Information, Appendix S5): centre of most scales on ventral half of flank, above anal fin, in dominant mature males (not considering bands, bars and iridescent lines) pastel yellow to golden; centre of most scales on dorsal half of flank, below dorsal fin, in dominant mature males (not considering bands, bars and iridescent lines) light grey; grey spots on head present; > 40 scales on lateral line; small scales; contact organs on anal fin of males present; and contact organs on most pectoral fin rays of males .

Above an overview of the history on how the genus Austrolebias was established. The table is taken from the paper by Alonso et. al, in 2023.

Etymology:

The name of the genus is composed of Titan and lebias. Lebias is from the Greek, meaning ‘small fish’, a name commonly used to compose generic names of cyprinodontiform fishes. In Greek mythology, the Titans (Greek: Τιτνες, Titânes, singular: Τιτάν, -ήν, Titán) were the pre-Olympian gods; they were the 12 children of the primordial parents Uranus (Sky) and Gaia (Earth) and famous for their strength and huge size. Named in allusion to the relative size of the fishes of this genus within Aplocheiloidei, bearing the largest species in this suborder of fishes, with T. elongatus reaching 15.5 cm SL (MACN 3826) and T. monstrosus 15 cm (MNK P-3301) (Osinaga 2006).

Distribution: Río de la Plata basin (excluding the middle and upper portions of the Paraná and Uruguay basins), Laguna Merín basin, Atlantic basins of eastern Uruguay and headwaters of the Mamoré basin, in Argentina, Uruguay, Brazil, Bolivia and Paraguay.

Literature:

Steindachner, F. 1881. Beiträge zur Kentniss der Flussfische Südamerikas (III). Sitzung der mathematisch- naturwissenschaftlichen Klasse von 5 Mai 1881. Anz. Akad. Wiss. Wien, 18 (11): 98.

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 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 comments.