Brittle star
Brittle stars do not use their tube feet for movement, but instead use muscles in their long, thin arms to go around rocks. Ophiurids move quickly when disturbed, and are faster movers than starfish. In living ophiuroids the plates are linked by longitudinal muscles. Ophiurid arms only move horizontally. The way their plates interlock prevents the arms from moving in any other plane.p64 In contrast, basket star arms can move vertically. These movement patterns are distinct, and separate the groups.