project, and five "interambulacral areas" between them. The mouth is near the centre or on the margin of the tegmen, and ambulacral grooves lead from the base of the arms to the mouth. The anus is also located on the tegmen, often on a small, elevated cone, in an interambulacral area. The theca is relatively small and contains the crinoid's digestive organs.

The arms are supported by a series of articulating ossicles similar to those in the stalk. Primitively, crinoids