Enchytraeidae (Oligochaeta) from taiga and tundra habitats of northeastern U.S.S.R.

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Abstract
The terrestrial Enchytraeidae were studied at 2 sites in northeastern USSR, 1 in taiga forest (Magadan) and 1 in tundra (Chaun Bay). Twenty-two taxa are reported, 13 at Magadan and 17 at Chaun Bay. Following review of the original descriptions and specimens, we designate Mesenchytraeus primaeuus Eisen, 1878 as type species for the genus. Five new species of Mesenchytraeus are described: M. diverticulatus from Magadan and M. chaunus, M. tundrus, M. kontrimavichusi and M. svetae from Chaun Bay. M. diverticulatus has an esophageal expansion and intestinal diverticula that are unique within this genus. Another new species with complex nephridia in segment II is described, but left in uncertain generic position. Henlea diverticulata Cejka, 1912, known previously only from the New Siberian Islands, occurred at Chaun Bay. Bryodrilus arctica (Bell, 1962), known only from St. Lawrence Island [USA], was found at Magadan and Chaun Bay. The other species are circumboreal in distribution. The enchytraeid fauna of northeastern USSR is similar to that of arctic and subarctic Alaska. The rich complement of species of Mesenchytraeus is a unique feature of the Beringeal region. Both abundance and species richness were higher in tundra than in taiga forest.