Deep-sea echinoderms of the Sea of Okhotsk

New samples of abyssal echinoderms taken in the Sea of Okhotsk by the SokhoBio expedition have been examined and analyzed. Taking into account this new data, 34 echinoderm species are distributed deeper than 2000 m in the Sea of Okhotsk. Among them, 10 species are found in the Sea of Okhotsk for the first time, and 6 species are found in the abyssal zone of the Sea of Okhotsk for the first time. The species richness of the abyssal echinoderm fauna in the North-West Pacific areas (north of 30 degrees N and west of 180 degrees E) negatively correlates with the level of their geomorphological isolation: the higher the level of isolation of the area, the lower the species richness of its abyssal fauna. The number of echinoderm species in the abyssal zone is found to be 9 in the most isolated Sea of Japan, 34 species in the semi-enclosed Sea of Okhotsk, and 47 species in the least isolated Bering Sea. More than 58 species occur in the open North-West Pacific abyssal area. The new data on echinoderms indicates both submergence of the sublittoral-bathyal species and dispersal of the abyssal species through the deep straits into the Kuril Basin of the Sea of Okhotsk. Among the abyssal echinoderms of the Sea of Okhotsk, pseudoabyssal and true abyssal species account for similar to 24% and similar to 35% respectively. The influence of the Antarctic and West Pacific deep-sea centers of fauna redistribution is discussed.