Final answer:
Echinoderms use a water vascular system for essential functions, where water enters through a sieved opening called the madreporite, traveling to tube feet that enable movement and feeding.
Step-by-step explanation:
Echinoderms such as starfish and sea urchins have a unique circulatory system called the water vascular system, which they use for movement, gas exchange, and feeding. The water enters this system through a sieved opening called the madreporite. Water travels from the madreporite through the stone canal into a ring canal located around the mouth. From there, it extends into radial canals along each arm, and finally into numerous tube feet that extend outside the body. These tube feet can attach to surfaces with incredible strength, helping echinoderms to capture prey and maneuver within their marine environments.