Red (Strongylocentrotus iranciscanus) and Purple (Strongylocentrotus purpuratus) Sea Urchins ~ Sea urchins live in shallow waters from the low-tide line to 90 meters deep.  They prefer rocky ground without any extreme waves or too much sand or mud. A sea urchin's body is completely covered by sharp spines; these spines grow on a hard shell called the "test," which encloses the animal. A sea urchin's diet consists of brown and green algae and decayed matter; if food lands on an urchin's back, the tube feet pass the food down to the urchin's mouth like a bucket brigade. Fun Fact! It is believed that the red sea urchin is among the longest living animals on Earth - living up to 100 years old (some may reach 200 years).