HYDRACHNIDS UNIONICOLA (HALDEMAN, 1842) IN BIVALVE MOLLUSKS IN THE KAMA BASIN

Water mites or hydrachnids are a large taxonomic group of arachnids that are widespread in various types of freshwater bodies. Most representatives of the mites of the genus Unionicola are closely related to bivalves at different stages of their life cycle (eggs and nymphae) and have an inhibitory effect on them. In the Russian Federation, infections of mollusks by these arachnids have been described in different regions but not on the Kama Basin territories. This article describes the invasion of the swan mussel Anodonta spp. by hydrachnids in some water zones of the Perm Region (the Chusovaya and the Kama Rivers). The infection prevalence was 0.2%, which may be related to the research period (autumn). Mite capsules were measured, and the average dimensions were 345.50±40.71 µm in length, 226.90±39.48 µm in width, and 7.40±2.79 µm in thickness. Mite cysts were located in dense clusters and single formations in the mollusk mantle. The histological examination showed the host mollusk response to the invasion that manifested in the form of chronic inflammation and tissue disorganization. Dreissena polymorpha was found to be free of invasion on these territories.