Q What are the corals?

Corals are characterized by their polypoid shape, slow growth and sessility and secretion of a solid skeleton made of calcium carbonate. Numerous coral individuals associate in intraspecific harmonic ecological interaction forming colonies with hundreds, thousands and even millions of beings. Water-permeated solid structures of these colonies, called reefs, work as true ecosystems for other living beings. The largest known coral colony is the Great Barrier Reef in the northeast coast of Australia. There are although many coral species whose individuals live alone and do not form colonies.