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Coral reefs are one of the oldest types of living systems on earth, and certainly one of the most spectacular. They are massive underwater structures formed by the limestone skeletons of tiny invertebrate animals. Reefs house a greater diversity of body forms, che ....

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.... of the reef. Over tens of thousands of years, chemical and mechanical changes turn the reef into true rock. The body of a coral animal consists of a polyp, which is the living portion of the coral. A polyp is a hollow, cylindrical structure attached at one end to a surface, the other end is a mouth surrounded by tentacles which gather food and can sting prey to paralyse it. Polyps live in colonies, which grow from 1 to 7 inches, depending on the species. Coral polyps are classified as animals. Microscopic algae live within the animal tissues in a symbiotic relationship. The algae turn sunlight into carbon and sugars, which are then available t ....