Nereididae (formerly spelled Nereidae ) are a family of polychaete worms. It contains about 500 – mostly marine – species grouped into 42 genera. They may be commonly called ragworms or clam worms .
Near mating time in most species, the rear part of the body becomes swollen with sperm or eggs. The worm leaves its shallow burrow on the sea bottom and, usually at night, releases sex cells near the water surface. After fertilization a spherical larva (trochophore) emerges from the egg. In some species mating occurs in the burrow. The female dies soon after.