Limnoperna fortunei (Dunker, 1857), during its invasion process in South America, has caused severe impacts both on natural environments altering native biodiversity, ecosystem structure and function-, and on man-made structures causing economic looses. Twenty-one samples were taken from the right bank of the Uruguay River, from tributaries of the Uruguay and Paraná Rivers, the drainage of the Esteros del Ibera Wetland. Based on this fieldwork, the presence of larvae and adults of L. fortunei was determined. Also, through the comparison of environmental characteristic with the known tolerance limits for the species, the possibility of its establishment in environments not yet invaded was determined. Most of the sampling stations have features that allow the development of stable populations L. fortunei, including the rivers that drain the Esteros del Ibera, allowing access of this invasive species to this important wetland.

Pomacea canaliculata (Lamarck, 1822) (Mollusca Gastropoda) mostra um grande alcance de distribuição natural na América do Sul, chegando até os 37º S (Buenos Aires, Argentina). Esta espécie foi introduzida propositalmente no sudeste da Ásia, por volta de 1980 e, mais tarde, se submeteu a uma dispersão de forma rápida intencional ou acidental em muitos países da região. Também foi introduzido na América do Norte, América Central e Havaí. Nesta contribuição se confere a presença de P. canaliculata na Patagônia e se considera a influência das alterações climáticas no novo estabelecimento desta espécie no local referido. Três coletas (entre setembro de 2004 até abril de 2005) foram realizadas (38º 58' 20.2" S and 68º 11' 27.3" W). Nelas encontraram-se dois exemplares adultos de P. canaliculada e numerosas desovas. P. canaliculata distribui-se naturalmente nas regiões das Bacias do Prata e Amazonas. O limite sul desta espécie foi estabelecido nas isotermas de 14 ºC e 16 ºC na província de Buenos Aires, com precipitações de 900 a 600 mm. Também são analisadas as variações na temperatura anual e a precipitação na Patagônia. As médias de temperatura mostram um aumento no decorrer de dois anos. Modificações importantes no regime de precipitação no norte da Patagônia poderiam ser benéficas para o estabelecimento das populações de P. canaliculata nesta nova área, onde as precipitações aumentaram o suficiente até atingir os valores similares aos da região mais austral citada para a distribuição desta espécie.

Pomacea canaliculata (Lamarck, 1822) (Mollusca Gastropoda) shows a large native distribution range in South America, reaching as far south as 37º S (Buenos Aires, Argentina). This species was deliberately introduced into Southeast Asia around 1980 and subsequently underwent a rapid intentional or accidental dispersal into many countries in the region. It was also introduced into North and Central America and Hawaii. In this contribution we record the presence of P. canaliculata in Patagonia, assessing the possible influence of climatic change in the new establishment of this species there. Three samplings (between September 2004 and April 2005) were carried out at 38º 58' 20.2" S-68º 11' 27.3" W. In the sampling we found two adult specimens of P. canaliculata and numerous egg clutches. Pomacea canaliculata is naturally distributed in the Plata and Amazon Basins. The southern boundary of this species has been established as the isotherms of 14 ºC and 16 ºC in Buenos Aires province, and precipitations of 900 to 600 mm/year. This study also analysed variations in annual temperature and precipitation in Patagonia. Average temperatures show an increase over the years, although not constantly. Important modifications in precipitation regime in northern Patagonia, triggered by global climatic changes, could be beneficial for the settlement of populations of P. canaliculata in this new area, where precipitation increased enough to reach values similar to those in the southernmost area of distribution of this species.

Pomacea canaliculata is a common gastropod in freshwater habitats from Central and Northern Argentina, extending northwards into the Amazon basin. Several Platyhelminthes have been reported associated to P. canaliculata, sharing an intimate relationship with this gastropod host. The objectives of this study were to describe the symbiotic species assemblages associated to P. canaliculata in the study area, and to disclose differences among them. Samples were taken in three typical small streams and one artificial lentic lagoon, all connected with the Río de la Plata estuary. The 81.53% were infested with different symbiotic (sensu lato) species. Among the Platyhelminthes, the commensal Temnocephala iheringi Haswell, 1893 was highly prevalent in all samples, always in the mantle cavity. Four trematode taxa were recognized: (a) metacercariae of Echinostoma parcespinosum Lutz, 1924 in the mantle cavity and sporocysts in the digestive gland; (b) metacercariae of Dietziella egregia (Dietz, 1909) in the pericardial cavity; (c) unidentified xiphidiocercariae and (d) unidentified sporocysts and furcocercariae in the digestive gland. Nematode larvae and oligochaetes were found in two localities in the mantle cavity. Among the Annelida, Helobdella ampullariae Ringuelet, 1945 was found in the mantle cavity and lung of snails only from one locality. Our results show that although some of the symbionts are present in all localities, others are restricted to some particular ones, whether in their absolute numbers or in their relative abundance. Thus, each hosting population at the studied localities may be defined by the particular combination of symbionts that bears.