The Red Pencil Urchin (Heterocentrotus mammillatus) has long red spines that are covered with a thin layer of living tissue. The spines were once used to write on slate, in place of chalk; the native Hawaiians carved the spines as well. A tiny red Commensal shrimp may sometimes be found among its spines.

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