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The study of bathymetry, macrozoobenthos abundance and the Russian desman population has been performed in the water bodies located in the Prisurskiy State Nature Reserve buffer zone (River Sura lower reaches floodplain). Twenty-one water bodies were examined in total. In six lakes, Desmana moschata (Russian desman) was absent. In nine lakes, the settlement density was less than 5 burrows per 1 km coastline. And in six lakes, the settlement density was high (i.e. more than 5 burrows per 1 km). The studied parameters of the lake basin included the depth of the lake, the water acidity (pH), dissolved oxygen concentration, the type of the plant cover of the shoreline (forest, shrub, steppe), and anthropogenic load. The taxonomical analysis and individual weighing of the animals in the macrozoobenthos samples were performed. All the parameters were then included to an analysis of the Russian desman density. The factors affecting the density of the Russian desman burrows were revealed. The water bodies having more than five burrows per 1 km along the shoreline are characterised by a higher abundance of macrozoobenthos and especially by the highest mollusk biomass. In turn, the abundance of mollusks, the main food, depends on the dissolved oxygen concentration in the water, trophic state of the lake, and the bottom slope. The highest density of the Russian desman was registered in the lakes characterised by a high biomass of the gastropods Lymnaea stagnalis and Viviparus (Contectiana) contecta. It was noticed that the Russian desman preferred to inhabit wide-course water bodies characterised by a high density of trees or bush along the shoreline. Therefore, the factors mentioned above may appear as the indirect characteristics of the water body with optimal habitat conditions for the Russian desman. Other water body characteristics, such as depth, may define the temporary optimum conditions for the Russian desman inhabiting. The combination of different conditions in a certain area allows the Russian desman to choose suitable water bodies, depending on the annual climatic conditions. There is a combination of a steppe (meadow) and forest areas in the River Sura lower reaches floodplain. Thus, this floodplain may be named as the most suitable for the Russian desman inhabitance.

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The article presents a comparative description of previously unknown morphological features of species of the genus Heterocope Sars 1863 inhabiting the territory of Russia. Using the SEM capabilities, the genital plate, structure, and of the P5 armament for the Heterocope soldatovi Rylov 1922 female and male and the genital plate of Heterocope saliens (Lilljeborg 1863) were described in detail. For the first time, information on the oral appendages of these species is presented. A comparative analysis of the morphological and morphometric differences between females and males of different Heterocope species was carried out, and a general identification table was compiled. Based on modern data, the boundaries of species ranges were specified.