Denis V. Tikhonenkov

Species diversity of centrohelid heliozoans in different types of freshwater bodies (forest lakes, floodplain lakes, sphagnum bogs, and river) in the Middle Russian forest-steppe was studied. The morphology of cell coverings (scales and spicules) were observed using scanning and transmission electron microscopy. A total of 20 species of  centrohelid heliozoans from five families (Acanthocystidae, Pterocystidae, Raphidiophryidae, Raphidocystidae, and Choanocystidae) and six genera (Acanthocystis, Raineriophrys, Pterocystis, Raphidiophrys, Raphidocystis, and Choanocystis) as well as unidentified Centrohelea species and a Heterophrys-like organism were found. Morphological descriptions and electron micrographs are provided. The most common species were Acanthocystis nichollsi, Raphidiophrys capitata, and a Heterophrys-like organism. The highest species diversity was observed in terrace forest lakes, whereas the lowest was seen in sphagnum bogs. Four species (Acanthocystis costata, A. elenazhivotovae, A. mikrjukovii, and A. spinosa) were found for the first time since their original description. Three species (Acanthocystis spinosa, Raphidiophrys capitata, and Pterocystis pulchra) are new records for Russia. The distribution of the observed morphospecies confirms the cosmopolitanism of many centrohelids and highlights the importance of the type of water body and microbiotope in forming the species composition. The obtained data on the morphology of studied scales supplements our knowledge of the intraspecific variability of centrohelid heliozoans.

We studied the diversity of heterotrophic flagellates from the sandy sediments of the Yangtze River, sandy and silty sediments of Donghu Lake, soil, moss and litter from the Luojiashan and Moshan hills as well as litter from the floodplain near Donghu Lake in April 2010. Sixty-seven heterotrophic flagellate species were identified by means of phase and interference contrast light microscopy and transmission electron microscopy. The majority of the observed flagellates were bacterivorous. Local species richness of river sediment communities was significantly lower than that of lake sediments and terrestrial habitats. The communities from the terrestrial habitats were more heterogeneous than those from freshwater sediments. Common species for the aquatic habitats were Rhynchomonas nasuta, Paraphysomonas sp., Neobodo designis, N. curvifilis, Bodo saltans and Spumella spp. In the soils only Spumella spp. was found in the majority of samples. Most characteristic taxa for the lake sediments were Helkesimastix faecicola, Petalomonas minuta, P. pusilla, Diphylleia rotans, Amastigomonas caudata. Amoeboflagellates such as Cercomonas angustus, C. granulifera, Paracercomonas crassicauda were specific for the terrestrial habitats. There were no specific taxa in the river sediments. The majority of the heterotrophic flagellates identified in this survey have been noted in China earlier. They are common (and usually predominant) for other regions in both freshwater and soil habitats.