Bristle worms are annelids that have a segmented, long body. Each segment has a pair of appendages with bristles. They range in size from less than an inch in length to two feet in length and they live in an aquatic environment. They use their muscles to extend and contract in the process of peristalsis to move. The pair of extensions on each segment of the bristle worm is called a parapodia and they are used to help them move as well.