Any of numerous small, sedentary cnidarians (coelenterates) of the class Anthozoa. Corals often form massive colonies in shallow sea water and secrete a cup-shaped skeleton of calcium carbonate, which they can retreat into when in danger. Corals are related to the sea anemones and have stinging tentacles around the mouth opening that are used to catch prey.
A hard, stony substance consisting of the skeletons of these animals. It is typically white, pink, or reddish and can form large reefs that support an abundance of ocean fish.