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a genus of polychaete worms of the family Nereidae. They are found primarily in the littoral zones of seas. Of the approximately 150 species, about 15 are encountered in the seas of the USSR. From 1939 to 1941 a mass resettlement of Nereis diversicolor from the Azov Sea to the Caspian Sea was conducted to increase the food base for commercial fishes in the Caspian. The worms have been successfully acclimatized to the Caspian Sea and now play an important role in feeding sturgeon and other fishes.