Bipolarity, its history and general interpretation are investigated and discussed herein. Apart from the classical view, namely that a bipolar distribution is a peculiar biogeographical phenomenon, we propose that it is ecologically controlled too. This approach was used for bipolarity assessment within the following groups: Phaeodaria, Nassellaria, Spumellaria (Radiolaria) and Medusozoa (Cnidaria). We recognize 46 bipolar radiolarian species and three radiolarian genera. However, although species concepts in radiolarians are relatively stable and well known, the high-rank taxonomy of radiolarians is still not well defined. Caution should therefore be taken in the interpretation of distribution data at a taxonomic level higher than the species. In the Medusozoa, bipolarity is observed for 23 species and 32 genera. The different ways in which bipolarity can develop are discussed under the different groups, but preference has been given to the recent and most probable routes of migration. In our investigation of the bipolarity phenomenon, we reviewed more than 400 articles dealing with taxonomy, ecology and biogeography of the modern fauna in both groups.

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For the first time the invertebrate fauna of the near-':~ottom layers of the Laptev Sea (Siberian Arctic) was studied by means of a specially designed devicethe benthopelagic sampler that was attached to an Agassiz trawl. Cnidarians, annelids, mollusks and arthropods were identified to species level and comprised 139 species in total. Fifty-one species are registered in the L~.ptev Sea for the first time and seventeen species are t/cue first records for the Arctic Basin. Species are characterized as pelagic, benthic and suprabenthic (benthopelagic, nektobenthic, epibenthic) species.