In some species the bristles can grow to considerable size. This could serve as a defence structure against predators. The larva lives free swimming in the plankton. It has a large flat head with cilia. With this it can suck in small food particles. After they become adults they start their lives on the bottom of the sea. Some will live buried in the mud. Many of them build special tubes for protection. Others move around searching for prey. A large group of polychaetes, the tube worms (Serpulidae), live in tubes attached to a substrate. They are beautiful creatures since they develop a large feathery crown of tentacles to capture plankton.
But not all bristle worms are so gentle and elegant. The last page will show you there are Polychaetes that are fierce and who will not hesitate to eat members of their own species.