In spite of the common occurrence of Hippeutis complanatus (L.) in some regions of Poland, it is considered to be a rare species with scattered sites. A study on its life cycle and shell growth in various conditions was possible due to the existence of very abundant populations in several woodland ponds of Silesia. The snails breed twice in a lifetime, and two generations reproduce in one year. The main breeding period is July/August. Some individuals breed also in the spring of the next year. The first appearance of the smallest individuals is clearly related to the water temperature.
The water bodies formed in forest complexes are characterised by a significant degree of isolation from other aquatic environments as well as from urban agglomerations. In industrial areas, they are refuges of biological diversity. The long-term ecological research carried out in woodland ponds has allowed us to identify a new site of the occurrence of Placobdella costata (F. Müller) (Hirudinida: Glossiphoniidae) in Poland, the fourth in the southern part of the country. Furthermore, ecological information about the habitat and accompanying freshwater leeches are given.