We have examined samples collected by the trans-siberian Swedish-Russian Ecology Expedition 1994, and critically evaluated the relevant literature and existing museum collections from previous expeditions to Siberia. Eleven species are described as new to science and the total number of enchytraeid species recorded from the Palearctic tundra is now 56. This indicates a species richness comparable to that of terrestrial habitats in ecologically more heterogeneous temperate regions. In the genera Mesenchytraeus, Henlea, Bryodrilus and Cognettia species diversity in the tundra is even higher than in temperate regions, which is contrary to the generally accepted poleward decline in diversity. The genera Fridericia and Achaeta follow the normal pattern with only few species in the Arctic. It is concluded that the Palearctic tundra in general and the Amphi- Beringian region in particular harbour a rich endemic fauna with a strong dominance of Mesenchytraeus and Henlea species.
