The molluscan fauna of the Syoyakha (Zelenaya) River remain poorly explored even though the Syoyakha is one of
the biggest rivers on the Yamal Peninsula. The Syoyakha River is remarkable for its high fish stocking capacity and it
plays an important role in the seasonal distribution and migration of commercial fish species. Freshwater mollusks are
known to be a major component of freshwater ecosystems and they make up a part of the diet of many commercially
important fish species. The species composition of the mollusks inhabiting the lower reaches of the Syoyakha River has
been studied. Five bivalve species of the family Sphaeriidae were found, namely Sphaerium corneum (Linnaeus, 1758),
Pisidium casertanum (Poli, 1791), P. globulare (Clessin in Westerlund, 1873), P. lilljeborgi (Clessin in Esmark et Hoyer,
1886) and P. dilatatum (Westerlund, 1897). In general, the molluscan fauna of the lower reaches of the Syoyakha River
are taxonomically poor, which can be considered typical of freshwater invertebrate communities living at high latitudes.
Another reason for the decline in species diversity may lie in the absence of any large transit watercourse in the basin
in question allowing northward dispersion of the mollusks. The average density of mollusks in the watercourse stretch
under study varied from 98.9 ind./m2 to 620.5 ind./m2. P. globulare settlements had the highest recorded density of
1,442.9 ind./m2. The mollusks are confined to clayey, silty and sandy substrates with remnants of vegetation. The fauna
is basically formed by widespread Palearctic and Holarctic mollusk species that have adapted to the extreme conditions
of the Arctic. The findings may be used for hydrobiological and fishery characterization of the watercourse given that
the recorded species of S. corneum, P. globulare, P. lilljeborgi, and P. dilatatum are a major food item for important fish
species, such as cisco, vendace, char, muksun, etc.