Coral
Corals are marine plants and animals from the class Anthozoa and live as small sea anemone-like polyps, typically in colonies of many other identical individuals. The group includes the important reef builders that are found in tropical oceans, which secrete calcium carbonate to form a hard skeleton.
Many people beleive that coral is a single organism, but it is actually made up of thousands of individual, genetically identical polyps, each polyp only a few millimeters in diameter. Over thousands of generations, the polyps lay down a skeleton that is characteristic of their species. A head of coral grows by asexual reproduction of the individual polyps. Corals can also breed sexually by spawning, with corals of the same species releasing gametes simultaneously over a period of one to several nights around a full moon.
Although corals have the ability to catch plankton using stinging cells on their tentacles, these animals usually obtain most of their nutrients from symbiotic unicellular algae called zooxanthellae. Most corals depend on sunlight and grow in clear and shallow water, typically at depths under 60 m (200 ft).
These corals are responsible to the physical structure of the coral reefs that develop in tropical and subtropical waters, such as the enormous Great Barrier Reef off the coast of Queensland, Australia. Other corals do not have associated algae and can live in much deeper water, such as in the Atlantic, with the cold-water genus Lophelia surviving as deep as 3000 m.