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a family of polychaete worms. The body length is from 4 to 90 cm (most often 5–10 cm). Of the approximately 350 species, 30 are found in the USSR. The worms live predominantly in burrows in the littoral zones of seas; some can tolerate extreme desalination. Nereids are omnivorous. When approaching sexual maturity, many species are transformed into heterone-reid forms; in some the eyes and parapodia become unusually enlarged, swimming chaetae appear, and the worms rise to the surface of the water for reproduction. Nereids serve as food for fish and, during the reproductive period, for many birds.