Most bristle worms found in coastal plankton are larvae of bottom dwelling worms, but there are some families that are completely adapted to life in free water, such as the worms of the genus Tomopteris. These are beautiful, bizarre animals that can also grow very large.
Tomopteris are almost transparent. The first and second segment of the body is merged into two palps. The worms have two eyes. The next segment contains a few very long sensory hairs. The next segments consist of paddle-shaped outgrowths (parapodia) with which the worm can swim fast. These parapodia can produce a yellowish light (bioluminescence). The species Tomopteris helgolandica, common in the North Sea, has a long tail that most related species miss.