Ruby brittle star on coral off the shore of the Cayman Islands (© Hal Beral/Corbis)

Christmas tree worms growing on coral (© Reinhard Dirscherl/Corbis)

Fairy basslet fish dart among blooms of lettuce coral near the Phoenix Islands, Kiribati, Micronesia (© Paul Nicklen/National Geographic/Getty Images)

Staghorn coral, Great Barrier Reef, off the coast of Australia -- Frans Lanting/Corbis ©

Deepwater mushroom soft coral (Anthomastus ritteri) off the coast of California, in the Pacific Ocean -- Mark Conlin/Photolibrary ©

Collare butterflyfish and soft coral in Surin Islands Marine National Park, Thailand -- F. Stuart Westmorland/Corbis ©