Crinoids
Uniquely among echinoderms, crinoids have no madeporite. Instead, the oral surface is dotted within numerous minute ciliated funnels that run into the main body cavity. The ring canal has several small stone canals, located between the arms of the animal, but these open into the body cavity, and thus are only indirectly connected to the outside.
The five radial canals run into the arms and branch several times to supply all of the individual branches and pinnules lining the arms. As in other echinoderms, the radial canals give rise to lateral canals, but there are no ampullae, and clusters of three tube feet branch from the ends of each canal, except around the mouth, where they are found singly. In the absence of ampullae, water pressure is maintained by the ring canal, which is surrounded by contractile muscle fibres.
Read more about this topic: Water Vascular System