Sea urchins inhabit rocks or mud along the seashores.
The purple urchin ranges from Alaska to Cedros Island off the coast of Baja California. Although it is mostly a subtidal species, the purple urchin is found intertidally on almost barren rock. Sea urchins are closely related to sea stars and brittle stars. The movable spines are purple and the most conspicuous of the three. All of the appendages are sensitive to touch and may also respond to chemicals released into the water by predators.