Amazing..
epitoky: a portion of the bristleworm becomes packed with eggs or sperm and becomes highly specialised for swimming, some even developing eyes! This portion is called the epitoke. At mating time, the epitoke breaks off from the main worm and can move about on its own. Swimming to the surface, it is joined by the epitokes of other bristleworms. At the surface, the epitokes burst apart, releasing eggs and sperm for external fertilisation. In this way, the worms can reproduce without exposing the rest of their bodies to danger. However, while an epitoke might be a new segment produced by the animal, sometimes the entire animal is remodelled into an epitoke and rips itself apart during mating. Mating is usually triggered by the lunar cycle.