Benthic freshwater testate amoebae assemblages (Protozoa : rhizopoda) fromLake Dongting, People's Republic of China, with description of a new species from the genus Collaripyxidia

A total of 42 testate amoebae species and varieties were identified in sedi ment samples taken from three stations (L, O, R) around the outlet of Lake Dongting to the ChangJiang (Yangtze) River. From these species, Collaripyxi dia dongtingiensis sp. n. is new to science and 25 are new to the testate a moebae fauna of the People's Republic of China. The most numerous were repr esentatives of the genus Centropyxis, followed by Difflugia and Cyclopyxis. Centropyxis aculeata is the most dominant species in the lake (Station L), while Plagiopyxis callida in both the outlet (Station O) and the river (St ation R). Each habitat has peculiar testate amoebae assemblage, only three species, Centropyxis aculeata, Centropyxis ecornis and Phryganella acropodi a var. depressa, have been observed at all habitats. The greatest total abu ndance and biomass values were observed at the outlet, while the smallest o nes in the river. From the lake to the river, both number of species and th e Shannon-Weaver diversity index values are decreasing, although the equita bility index of the outlet habitat was a little lower than that of the rive r habitat. The main cause for the decreasing diverse testacean assemblages from the lake to the river may be the unstable environment resulting from h igh water velocity.