Anthozoa in the phylum Cnidaria, which also includes sea anemones and jellyfish.
Corals exist in warm seas, at moderate depths with sufficient light.
Some coral is valued for decoration or jewellery, for example, Mediterranean red coral Corallum rubrum . The algae obtain carbon dioxide from the coral polyps, and the polyps receive nutrients from the algae. Corals also have a relationship to the fish that rest or take refuge within their branches, and which excrete nutrients that make the corals grow faster. The majority of corals form large colonies although there are species that live singly. Their accumulated skeletons make up large coral reefs and atolls.