Gyraulus

Abstract: A large number of planorbid snails are now commonly transported by man mainly through the aquatic plant trade. However, only a restricted number of species establish viable populations in a new habitat and a more restricted number spread. Only five planorbid species can be ranked in this last category and can be considered as pests because of their role in the transmission of parasites to humans or domestic animals: Biomphalaria glabrata, B. straminea, B. tenagophila, B. pfeifferi and Indoplanorbis exustus. The neotropical B. glabrata, B. straminea and B. tenagophila have proven their capacity to invade another continent sometimes creating new transmission foci. The African B. pfeifferi and the Indian I. exustus have also expanded their distribution area with long-distance dispersal. Other planorbid species, i.e. Helisoma duryi, Amerianna carinata and Gyraulus spp. have been able to establish viable populations, but not to spread, presumably because they are limited to specific habitats or/and display poor competitive abilities.

Abstract: The ecology of the aquatic gastropods Bithynia tentaculata, Gyraulus albus, Planorbis planorbis and Lymnaea peregra in North West England was investigated over 13 months at sites chosen for their wide range of water chemistry. Multiple regression analysis was used to determine the significance to the mollusc distributions of a variety of physico-chemical factors. Biotic factors were not considered. The species had similar life cycles, with little difference between populations within a species. B. tentaculata could live for over a year, and the major water chemistry variable was potassium (+), where the sign is that of the regression coefficient. G. albus could also survive into a second year and the major variable was mud substratum type (+). Rock substratum type (-) was the most important factor for P. planorbis. There was a slight difference in the life cycles of L. peregra in hard and medium compared with soft waters and the major water chemistry variable was magnesium (-).