This purple sea urchin cluster, living near the surface, is interesting as these animals have very strong spines and over time actually dig out their protective dwellings into the surrounding rock. The purpose of these deep depressions is to protect the purple sea urchins from crashing waves and violent storms that hammer the open ocean coastline. The purple sea urchin (Strongylocentrotus purpuratus) has a range that includes Japan, as well as northern Alaska to northern Mexico, and they can grow to 6 inches (15 cm) across. These urchins live in the intertidal zone down to around 215 feet (65 m) of depth, and may live as long as 70 years of age.
This blood star has chosen a tricky path to travel along near the spines of the surrounding purple sea urchins.