Remarks on Gammarus lacustris G.O. Sars, 1863, with description of Gammarus varsoviensis n. sp. (Crustacea, Amphipoda)

On the ground of the examination of a large material from Poland and from other countries, the variability of Gammarus lacustris G. O. Sars, 1863, is discussed. Gammarus wigrensis Micherdziński, 1959, is in the author’s opinion an immature G. lacustris. A detailed description of Gammarus varsoviensis n. sp. is given. Some ecological and biological data on both species are discussed, as well as their distribution in Poland