The Red Pincushion Urchin (Salmacis bicolor.) also known as the bicolor urchin is a small Urchin that can be found among the Atlantic Ocean. They reach a maximum size of 3-4 inches and feed on a variety of detritus, as well as algae. They are typically stationary during the day, but will come out around twilight to scavenge for food. Aristotle 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. Some fish will lay eggs among urchins, relying on the spines to keep them safe from predators.