The upper sections of the watercourses were inhabited by small numbers of six taxa of Gastropoda. An increase in the number of taxa were observed in sections in contact with flow-through lakes. In the watercourses there occurred species typical for the lakes of this area. Only Ancylus fluviatilis (Gastropoda) and Unio crassus (Bivalvia) were found solely in the running waters.
In the littoral of an oligotrophic Hańcza Lake molluscs were the second most abundant group (next to Asellus aquaticus (L.)) of invertebrate macrofauna on Characeae (17%–34% total abundance). Thirteen taxa were found, with a distinct dominance of Dreissena polymorpha (Pall.); in some sites the proportion of Valvata cristata O. F. Müll. or the genus Pisidium was considerable. A rare relict Marstoniopsis scholtzi (Schm.) was sporadic.
Sixteen taxa of Gastropoda were found in nine isolated lakes in the Suwalski Landscape Park. The species composition of snails and the number of species were different in individual lakes, but in this group of lakes were similar to those found in the interconnected lakes in this area. Bivalvia were represented by the family Sphaeriidae only.
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