What body system lets sea stars move using hundreds of tiny tube feet?

The water vascular system lets sea stars move using hundreds of tiny tube feet.

This hydraulic network is a defining feature of echinoderms, the animal group that includes sea stars, brittle stars, sea urchins, and sea cucumbers. In a sea star, seawater enters through a sieve-like madreporite and travels through canals to the tube feet.

Muscles and fluid pressure work together to extend and retract the tube feet. The feet can attach to surfaces, allowing a sea star to crawl, climb, hold prey, and exchange gases. Many tube feet operate together, so movement does not depend on a single central limb.

The system is not simply a blood circulatory system. It is a separate hydraulic apparatus with roles in locomotion, feeding, respiration, and sensory contact. Sea stars have radial body organization, usually with five arms, although some species have many more.