From the mud to the tree: phylogeny of Austrolebias killifishes, new generic structure and description of a new species (Cyprinodontiformes: Rivulidae) Author Alonso, Felipe Instituto de Bio y Geociencias del NOA (IBIGEO), National Scientific and Technical Research Council (CONICET) - UNSa, Av. 9 de Julio 14, A 4405 BBA Rosario de Lerma, Salta, Argentina & Killifish Foundation, La Plata, Buenos Aires Province, Argentina Author Terán, Guillermo Enrique Killifish Foundation, La Plata, Buenos Aires Province, Argentina & Fundación Miguel Lillo - Unidad Ejecutora Lillo (CONICET), San Miguel de Tucumán, Tucumán, Tucuman Province, Argentina Author Alanís, Wilson Sebastián Serra Killifish Foundation, La Plata, Buenos Aires Province, Argentina & Sección Ictiología, Departamento de Zoología, Museo Nacional de Historia Natural, Montevideo, Uruguay & Centro Universitario Regional del Este (CURE) Sede Rocha, Rocha, Uruguay Author Calviño, Pablo Killifish Foundation, La Plata, Buenos Aires Province, Argentina Author Montes, Martin Miguel Killifish Foundation, La Plata, Buenos Aires Province, Argentina & Centro de Estudios Parasitológicos y de Vectores - [CCT-CONICET - La Plata] Centro Científico Tecnológico Conicet, La Plata - [Conicet] Consejo Nacional De Investigaciones Científicas y Técnicas, La Plata, Buenos Aires Province, Argentina Author García, Ignacio Daniel Killifish Foundation, La Plata, Buenos Aires Province, Argentina & Instituto de Limnología ‘ Dr. Raúl Ringuelet’ (ILPLA) - UNLP-CONICET, La Plata, Buenos Aires Province, Argentina Author Barneche, Jorge Adrián Killifish Foundation, La Plata, Buenos Aires Province, Argentina & Centro de Estudios Parasitológicos y de Vectores - [CCT-CONICET - La Plata] Centro Científico Tecnológico Conicet, La Plata - [Conicet] Consejo Nacional De Investigaciones Científicas y Técnicas, La Plata, Buenos Aires Province, Argentina Author Almirón, Adriana Universidad Nacional de La Plata, Facultad de Ciencias Naturales y Museo, División Zoología Vertebrados, La Plata, Buenos Aires Province, Argentina Author Ciotek, Liliana Administración de Parques Nacionales, Parque Nacional Campos del Tuyú (7103), General Lavalle, Buenos Aires Province, Argentina Author Giorgis, Pablo Administración de Parques Nacionales, Parque Nacional Campos del Tuyú (7103), General Lavalle, Buenos Aires Province, Argentina Author Cascioưa, Jorge Universidad Nacional de La Plata, Facultad de Ciencias Naturales y Museo, División Zoología Vertebrados, La Plata, Buenos Aires Province, Argentina text Zoological Journal of the Linnean Society 2023 2023-07-10 199 1 280 309 http://dx.doi.org/10.1093/zoolinnean/zlad032 journal article 266147 10.1093/zoolinnean/zlad032 684543f4-855c-492a-b163-a157473a187c 0024-4082 8326346 E1210342-9DBD-4D89-ABF5-1925792D0E14C Genus Acrolebias Costa, 2008 stat. nov. Acrolebias Costa, 2008 as a subgenus of Austrolebias . Type species: Cynolebias carvalhoi Myers, 1947 . Diagnosis: Acrolebias differs from all other genera of the Austrolebias genus group by unique male coloration consisting of golden body flanks with eight to nine purple-grey bars. Additionally, this genus can be identified by the following unique combination of characters: no contact organs on anal fin in male; bases of pelvic fins separated by small interspace; anal fin short in females; urogenital papillae not attached to anal fin; dorsal fin origin anterior to anal fin origin; 21 or 22 dorsal fin rays in males, 16–18 in females; 21or 22 anal fin rays in males, 16–18 in females; and 27–29 longitudinal series scales ( Costa 2006a ). Differential diagnosis: The genus Acrolebias 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 being non-hyaline in adult males (vs. hyaline in Amatolebias , Austrolebias and Garcialebias ); by the lack of contact organs on the anal fin of males (vs. present in Acantholebias and Cypholebias ); by the rostral region scaled and vertically directed suborbital bar (vs. suborbital bar posteriorly directed and anterior region of head near rostral neuromasts without scales in Megalebias ); by markings on the distal portion of the dorsal fin, if present, not fused (vs. present and fused in Argolebias ); and by unpaired fins dark grey on males (vs. with bluish to greenish iridescences in Matilebias ). Synapomorphies: We redefine Acrolebias as a monotypic genus that presents the following five morphological autapomorphies (see Supporting Information, Appendix S5): pastel yellow to golden centre of most scales on ventral half of flank, above anal fin, in males (1:2); male pelvic fin bases separated by an interspace (57:0); <14 abdominal vertebrae (169:0); dorsal radial of pectoral fin present (189:1); and flanks with well-defined and regular vertical dark grey bars (16:1). Included species: Acrolebias carvalhoi (Myers, 1947) comb. nov. Distribution: Upper Iguazú River basin.