Within the Loricariidae, the genus Hypostomus is one of the most diversified freshwater catfish groups. Using new se-quence data from the mitochondrial Control Region (D-loop) we examined the phylogeny of this genus. Our phylogeneticanalyses suggest that, in the Paraná river basin, species diversity in the genus Hypostomus has been shaped by two proc-esses: 1) by inter-basin diversification, generating groups of species that inhabit different basins, as a result of dispersalevents; and 2) via intra-basin speciation as a result of basin fragmentation due to past marine transgressions, which pro-duced groups of species within a basin. Using the D-loop as a molecular clock, each event of diversification was datedand linked with documented hydrological events or sea level changes. We also assessed the possible dispersal routes be-tween the Paraná and Uruguay rivers, in addition to the obvious dispersal route via the Río de la Plata estuary. Finally, wedescribe a new species of Hypostomus inhabiting Middle Paraná river, Hypostomus arecuta n. sp. This species can be sep-arated from all other Hypostomus by having light roundish dots on a darker background and by number of premaxillary/ dentary teeth.

Crenicichla taikyra, new species, is described from the middle río Paraná, Argentina. Crenicichla taikyra is distinguished from the other species of the genus by the following combination of characters: lower pharyngeal tooth plate stout, bearing molariform teeth, ascending arm of premaxilla longer than the dentigerous arm, posterior edge of preoperculum serrated, a well developed suborbital stripe, and absence of scattered dark dots on flanks. Molariform teeth on pharyngeal jaws is a derived character among Crenicichla species, however this character state has appeared several times in unrelated species.

ABSTRACT. The Potamotrygonidae family represents the only freshwater group of specialized elasmobranchs and is composed of 4 genera: Plesiotrygon, Paratrygon, Potamotrygon, and Heliotrygon. Individuals of Potamotrygon motoro were collected from the Paraná River at Ituzaingó (Province of Corrientes) in Argentina. Mitotic preparations were obtained using direct techniques and lymphocyte cultures. Chromosomes were studied with conventional Giemsa, C-band and nucleolus organizer region stainings. The diploid number and karyotype formulae were 2n = 66 with 33 homomorphic pairs (14M + 16SM + 22ST + 14A) in females and 2n = 65 with 31 homomorphic pairs plus 3 heteromorphic chromosomes (13M + 15SM + 23ST + 14A) in males. Heterochromatin was distributed at ©FUNPEC-RP www.funpecrp.com.br Genetics and Molecular Research 12 (3): 2368-2375 (2013) Sexual chromosome system in Potamotrygon motoro 2369 the pericentromeric regions of almost all chromosomes and in the telomeric and interstitial positions of some chromosomes. nucleolus organizer regions were multiple and located at telomeric regions. Because of the clear karyotype differences between the 2 sexes and the presence of 3 unpaired chromosomes in males, it is possible to suggest the occurrence of a multiple sex chromosome system, with male heterogamety (X 1 X 1 X 2 X 2 /X 1 X 2 Y). Further cytogenetic studies are required to develop a hypothesis about the origin of the multiple sex chromosome system in P. motoro.

During 2015, we collected several specimens of a cichlid tentatively assigned to Geophagus in Yacyretá reservoir in the Paraná river basin (Argentina). By means of morphological and molecular evidence, we identified these specimens as Gephagus sveni, a species known from middle portion of the Tocantins River. Here we report the presence of the genus Geophagus (sensu stricto) in Argentina for the first time.

During 2015, we collected several specimens of a cichlid tentatively assigned to Geophagus in Yacyretá reservoir in the Paraná river basin (Argentina). By means of morphological and molecular evidence, we identified these specimens as Gephagus sveni, a species known from middle portion of the Tocantins River. Here we report the presence of the genus Geophagus (sensu stricto) in Argentina for the first time.