Lake Barlineckie is one of the largest glacial lakes in the Myślibórz Lakeland, Surrounded by morainal hills vegetated mostly by beech forests, the lake is fed by three tributaries, one of which originates in the hills in the south and supplies the lake with cold and clean spring water. Numerous springs well up on the southern slopes and in the shallow littoral of the lake; for this reason, water temperature of Lake Barlineckie is lower in summer and higher in winter than that in other lakes. Collections for this work were made in spring and summer of the years 1992-1995. Molluscs were collected down to the depth of 80 cm from 9 sites, using a scoop net and by examining aquatic plants and submerged objects. Samples from transects I, II, and III were collected with a 400 cm² Ekman-Birge grab, at 1 m depth intervals down to 8 m. The study was aimed at describing the mollusc (Mollusca) fauna of 5 selected plant species representing assemblages of helophytes, nymphaeids, and elodeids in the shallow littoral of Lake Barlineckie; vertical distribution of the molluscs was examined as well. The collection consisted, overall, of 9 308 individuals contained in 110 samples. A total of 26 gastropod (Gastropoda) and 20 bivalve (Bivalvia) species were identified. In Lake Barlineckie, gastropods were mainly associated with plants: 60% of all individuals were collected from them. Phragmites australis, Potamogeton perfoliatus, Ceratophylum demersum, Myriophyllum spicatum, and Nuphar lutea supplied 22, 16, 10, 8, and 4% of the total number of gastropods, respectively. In terms of the species richness, the highest number of species was found on N.lutea (23 species), the lowest species richness being typical of P.australis (13 species). Bivalves were found to occur within 0.5-1 m depth range where a total of 20 species were identified. Down to the depth of 2 m, the number of species decreased by 50% and was further reduced with depth. The bivalves occurring at the deepest (at depths exceeding 7 m) were Pisidium henslovanum and P.nitidum; Dreissena polymorpha was found to uniformly inhabit the bottom down to the depth of 6 m; Unio tumidus and Anodonta complanata occurred down to the depth of 2 m at the sites located close to the direct supply of spring water. Anodonta anatina inhabited the shallow littoral within the depth range of 0.5-1 m. The abundance of gastropods and bivalves along the three transects demonstrated depth-dependent variability, both in spring and summer. Both the abundance and the structure of mollusc assemblages was closely related to phenological cycles of aquatic plants. Lake Barlineckie was found to support 11 bivalve species threatened by extinction, including Pisidium lilljeborgii, an early glacial relict.

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