Abstract
Three species of mysids (Crustacea, Mysidacea), Mysis litoralis, M. oculata, and M. polaris were present in plankton collections from the East Siberian and Laptev seas. Two or three of these species frequently occurred together in these neritic areas strongly influenced by the runoff from rivers, while only M. polaris and Boreomysis nobilis were found in the Arctic Ocean and adjacent areas of deep water which are covered by ice. The occurrence of M. litoralis and M. oculata each in two distinct groups, characterized by different body lengths and development of secondary sexual characteristics, indicates that more than one year is needed for maturation and that the breeding season is limited for these species in Siberian seas. Size differences in M. litoralis juveniles from the East Siberian and Laptev seas are probably attributable to different lengths of time between spawning and collection rather than solely to environmental differences between the two seas.
