The Sea Urchin Crab (Echinoecus pentagonus) is a parasite on the Banded Urchin (Echinothrix calamaris). The male crabs are small and hard to see among the spines; a single female lives in the rectum of the urchin (which is found on the top of the urchin), feeding on the urchin�s fecal pellets.

This urchin was photographed in about 40 feet of water off the south Kohala Coast near the Mauna Lani Resort on the Big Island of Hawaii.