Sea urchins live in the intertidal zone to 100 feet in depth. At low tide, they take shelter from waves in rock cavities. At other times they roam in search of their favorite foods, giant kelp and other algae. Urchins have hard, round shells called tests, covered with spines. Spines can break off in human skin and be painful and hard to remove. Related to sea stars, they have similar tube feet that stick out between their spines for maneuvering and capturing prey. They also have a central mouth with strong jaws and sharp teeth.