Crinoids - sea lilies and feather stars - possess a crown analogous to the discs of stelleroids with long arms, fringed by extensions called pinnules. Sea lilies have stalks which attach them to the substrate. Feather stars are stalkless and free living; they can crawl and even swim using their arms as paddles. Both mouth and anus are on the upper surface of the disc and crinoids are the only living echinoderms in which the oral surface is directed upward. The podia occur in ambulacral grooves which extend along each arm and pinnule. Both arms and pinnules are jointed and can be rolled up. The podia are covered in mucus and trap organisms suspended in the currents. The food is then swept down the grooves to the mouth. The sea lilies appear closest in form to the first echinoderms of 560 million years ago.
Antedon bifida – a British feather star is at the bottom right of the photograph.