What muscles do the musculature of small-bristle worms consist of?

Small bristle worms are loose, living bristle worms (polychaetes) that have developed sensory hairs on each segment into bundles of small, white, sharp, removable bristles for protection. Clusters of reddish, irregular branching filaments are part of their circulatory system. On the head is a fleshy plate called a caruncle; its size and shape are often the key to identifying species. These worms prefer to cover the rock during the day, but can sometimes be found crawling around the reef, where they feed on branched corals and gorgons. Their bristles can easily penetrate the skin and break, causing painful irritation.