Strongylocentrotus purpuratus,the purple sea urchin, lives on the west coast of North America from British Columbia, Canada to Ensenada, Mexico. This echinoderms (in the same phylum as sea stars and sea cucumbers) graze on algae that grow on rocks. They live from the intertidal down into the subtidal.
An urchin has an internal shell called a test. The urchin has its test covered with pedicellariae (small pincers), tube feet and spines. The spines are attached to the body of the urchin by ball-and-socket joints making them very movable. The predators of these urchins include otters, sea stars and sheephead fish. When a sea star gets close the urchin will move its spines so that its pincers can pinch the tube feet of the sea star causing the sea star to back off.
With the overfishing of the red sea urchin fishery in California, there has been expanded harvesting of the purple urchin. This urchin is much smaller than the red so the fishery is not very active. They are harvested for their gonads which are exported to Japan for sushi.