The larva may remain in the free water for a varying amount of time, and it may be feeding on small plankton or it may be living on the resources provided in the egg. Following this period the larva settles and goes through a more or less radical metamorphosis to the adult stage. In other cases, however, the female may not shed the eggs into the free water, but instead receive sperm and brood the young. These may then have a short free-swimming period, or they may hatch directly as small adults. The morphological variation is as high as the variation in feeding and reproductive modes.
Some polychaetes live in tubes, others are active and crawl or swim around.
Errant forms often are equipped with an armed or unarmed proboscis which can be everted to catch prey.