AbstractThe species composition and structure of bottom communities with a predominance of bivalve mollusks of the Portlandia genus, which are widespread on the shelf of the Russian Arctic, were analyzed. Molecular genetic analysis confirmed that Portlandia aestuariorum and P. arctica are valid species; it has been shown that all P. arctica from different regions belong to the same species regardless their morphological variations. Ten different variants of benthic communities from the White, Kara, Laptev, and East Siberian seas were described, in which P. aestuariorum and P. arctica play the dominant role. No associated species complexes have been identified for Portlandia spp. Communities practically do not have common species, and their composition and structure are determined by the selection of species with similar ecological preferences from the local fauna. The differences in communities are determined by both geographical and environmental factors.