Cyphoma gibbosum

The Cyphoma gibbosum, or Flamingo Tongue, is a species of Sea Snail. I spotted 8 of them today on a short snorkel around a nearby cove. They are about 1 inch long, and live at a depth of 6 to 45 feet (according to an identification guide). At first I thought they were a type of nudibranch, but as it turns out they have a shell. I had to read about them to find that out though - it's not often wise to touch things under water if you're not entirely certain what they are. The spotted pattern is a fleshy mantle that extends over their back. When retracted, it exposes a white-ish shell. Sort of like a snail in reverse. Only one of the 8 I saw had its mantle retracted.

Source: http://photography.nationalgeographic.com/photography/enlarge/flamingo-tongue-snail.html

They live on and eat soft corals and sea fans, and are preyed upon by a variety of fish. They are one of many animals that, if not checked by predation, can quickly overrun an ecosystem and deplete it of corals.