Epitokous

abrupt changes in the body structure of many creeping worms of the class Polychaeta. Epitokous occurs in the period of sexual reproduction, when the worms become adapted to swimming. It sometimes involves only those parts of the body containing eggs or sperm, usually the posterior segments. As a result there is a sharp division of the body into a sexless anterior section, or atoke, and a sexual posterior section, or epitoke. The latter usually detaches and swims independently, dispersing eggs or sperm.