The genus Potamolithus Pilsbry, 1896 (Gastropoda: Tateidae) on the Somuncurá Plateau, Patagonia, Argentina

The genus Potamolithus (Gastropoda: Tateidae) is endemic to South America where it is distributed mainly in the Ribeira, Itajaí-açú and Jacuhy Rivers in southern Brazil and the Uruguay River, part of the Paraná and Río de la Plata drainage systems. An exception to the pattern of distribution is Potamolithus valchetensis Miquel, 1998, which is endemic to the Valcheta Stream, Somuncurá Plateau, Patagonia, Argentina. Here we provide a review of Potamolithus from this plateau based on new samples and review of material deposited in collections. A new species, Potamolithus elenae, is named. The shell, head-foot, penis, pallial organs and radula are described. Differences between the new species and P. valchetensis include details in the shell, radula, body pigmentation and penis. A phylogeny using mitochondrial gene cytochrome c oxidase subunit I is provided which shows that Potamolithus is related to species in New Caledonia (Australasia), suggesting that the Tateidae has a Gondwanan distribution.Fil: de Lucia, Micaela. Universidad Nacional de la Plata. Facultad de Ciencias Naturales y Museo. División Zoología Invertebrados; ArgentinaFil: Gutierrez Gregoric, Diego Eduardo. Universidad Nacional de la Plata. Facultad de Ciencias Naturales y Museo. División Zoología Invertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentin

Distribuição sazonal e reprodução de Neocorbicula limosa (Maton) (Bivalvia, Corbiculidae) no Lago Guaíba, Rio Grande do Sul, Brasil Seasonal distribution and reproduction of Neocorbicula limosa (Maton) (Bivalvia, Corbiculidae) in the Guaíba Lake, Rio Grande do Sul, Brazil

<abstract language="eng">Neocorbicula limosa (Maton, 1811) is the only species of that South American genus that occurs in the hydrographic basins of Rio Grande do Sul State, Brazil. Seasonal quantitative collections between 1995 and 1996 in the lake Guaiba were accomplished, with the aim to know the reproductive dynamics and environmental preferences of populations of N. limosa. A substratum constituted by medium to coarse sands at an 'average depth around 2m shown to be favorable to installation of population of N. limosa. The largest population density (2.496 ind./m²) was registered in summer. Embryos at various development phases were registered inside individuals. The shell sizes of these individuals started from 8mm in length. The embryo's size could reach ¼ of the shell-mother's size, and their liberation occurs through the rupture of the gills