Urchins belong to a Class known as Echinoidea, which consists of creatures that have a skeleton made of ten plates covered with spines. Urchins have mostly round bodies with protective spines on their upperside and tubular feet and a mouth on the underside. Artistotle once wrote of the five parts of the Urchin's mouth: "In reality the mouth-apparatus of the urchin is continuous from one end to the other, but to outward appearance it is not so, but looks like a horn lantern with the panes of horn left out." This holds true today as the mouth of the Urchin is referred to as "Aristotle's Lantern". The mouth of the Urchin is used to scrape algae from rockwork. The spines of the Urchin are a defense mechanism that are barbed like that of a fish hook and can inflict serious pain to the predator. These spines can either come to a sharp point or can be stubby and blunt.Photo by saltwaterfish.com member, Zexx: Natalie Cervantes.