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The Corals are characterized by their polypoid shape, sessility and slow development and secretion of a solid skeleton made up of calcium carbonate. Many coral individuals relate in intra-specific harmonic ecological interaction making colonies with hundreds, thousands and even millions of living-beings. Water-permeated solid structures of such colonies, termed as reefs, work as true ecosystems for the other living-beings. The biggest identified coral colony is the Great Barrier Reef in the northeast coast of Australia. There are though many coral species whose individuals live alone and do not make colonies.