Morphological diversification of alien and native aquatic snails of the genus Physa and Aplexa (Gastropoda: Physidae) of Western and Central European range.

This is the first comparative study on alien and native Physidae (Gastropoda: Heterobranchia) from Western and Central Europe. Morphology, ecological features and distribution are presented for each physid species. We analysed taxonomical features of physid snails from Europe in great detail. Scanning electron microscopy (SEM) methods were used to elucidate the external morphology of the shells of physid gastropods that occur in Western and Central Europe. On comparison we found significant differences in the external morphology among the species. Morphological analyses facilitate the recognition of variations of physid shells. An interspecific similarities were noted within Physidae while interspecific differences were identified in the morphology of apex and spires. The lowest intraspecific variability in shells was noted between particular individuals of P. fontinalis and A. hypnorum. The most characteristic features and differences of representatives of Physidae are presented and discussed. This is especially important for the identification of Physa gyrina and the worldwide invasive species Physa acuta which resemble each other in shape and are difficult to distinguish. We also present a new identification key for physid species, including the results of ecological assessment and discuss current distribution of these species in Europe.

Freshwater alien species Physella acuta (Draparnaud, 1805) - A possible model for bioaccumulation of heavy metals.

In this study we focused on Physella acuta, an alien snail species in order to determine their ability of bioaccumulation of heavy metals in their shells, bodies, the difference in accumulation in relation to age classes, and the influence of ecological variables on the community composition and density. On the basis of the results of ecological, toxicological, and experimental analyses we aimed to study the potential invasive features of P. acuta in comparision with the native species Stagnicola palustris. The content of Cu and Zn in the substratum and ammonia in the water was strongly related to the patterns of distribution of P. acuta. The content of Cd, Pb, and Cu in the shell fraction was always significantly lower than in the body fraction. A comparison of accumulation with respect to the size classes of P. acuta indicated that the lowest metal concentration in the body was typical for the largest individuals, except for Zn. Metal content in the bodies of the native species did not differ from the content measured in their analogous group of the largest individuals of P. acuta. The lowest value of bioaccumulation factor (BAF) was found for the large class of specimens of this species for each metal. A distinct decrease in the value of BAF in relation to the size of snails was found for cadmium. A 100% hatching success found in masses collected from pond confirmed the high reproductive potential of P. acuta which can be a factor that promotes its invasive features following its ability to occur in very high densities, but not necessarily the ability of metal accumulation in the body. Physella acuta can be used as a model organism in the studies on the accumulation of heavy metals however, the extend of accumulation can differ among the age classes. Because of the high tolerance of P. acuta to heavy metal pollution, in the future this species can be found in significantly polluted habitats, inhabiting free ecological niches, and occurring in high densities in snail communities.