Five species of molluscs, including Melanoides tuberculata (O. F. Müller, 1774) and Helisoma duryi (Wetherby, 1879) occur in a water basin, in the hothouse of the Botanic Garden in Cracow. The first mentioned snail inhabits a. o. the Near East and Eastern Africa while the latter one-Florida and Southern Africa. Another species-Physa acuta Draparnaud, 1805 spreads from the Southern Europe and for 30 years is adapted to polluted and heated waters in industrial regions in Southern Poland.