The present paper is based on materials collected in Chukchi Sea and adjacent southern edge waters of Canada Basin, Arctic Ocean during the period from July to August 1999 on the icebreaker, the R/V “Xuelong”, by the Chinese First Arctic Scientific Expedition. Totally, 8 species of pelagic Hydromedusae were identified, of which 4 species belonged to Anthomedusae, 2 species to Leptomedusae, 1 species to Trachymedusae and 1 species to Narcomedusae, the Neoturris breviconis is recorded for the first time in Chukchi Sea. Their principal morphological characteristics are described and illustrated. The 8 species of Hydromedusae occurring in the Chukchi Sea were all cold water species, of which 6 species belong to neritic species and 2 species to ocean species. According to the geographic distribution of species, they may be divided into three groups: Arctic species, Arctic-boreal species and Boreal-temperate species. From the view-point of zoogeography, species from these waters belong to the Arctic fauna.The abundance of Hydromedusae in Chukchi Sea was generally low, with a mean value of 108 ind.*10-2*m-3. Rathkea octopunctata and Aglantha digitale were dominant species. From the view-point of vertical distribution Aglantha digitale is inhabiting in the depth of 0 300 m and with the maximum in the depth of 50 m to 100 m.
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