Answer:
polyp
Coral polyps secrete a rock-like skeleton of calcium carbonate around them. Calcium carbonate is also the dominant consituent of the rock, limestone. Because modern corals live in large colonies, these skeletons can become quite large, sometimes forming reefs.the soft tissue decays which leaves a hard skeleton behind the skeleton also that was preserved as a fossil of ancient coral and the coral that exists today all belong to the order of Scleractinia (SCLER-ac-TIN-ee-a). in the past the fossils found today lead to the conclusion that their where other kinds of coral which are now extinct The order Rugosa was dominated by solitary corals in which each coral polyp had its own skeleton. Rugose means wrinkled or rough, and the outer surfaces of most rugose coral skeletons has a wrinkled appearance. Because some of the solitary rugose corals formed horn-shaped skeletons, they are called horn corals. Some Rugose corals also formed colonies and coral heads. The order Tabulata consisted entirely of groups of coral animals that lived in large colonies with a shared skeleton. These colonial corals grew in mounds, branching shapes, as chain-like shapes, and even in shapes resembling pipe organs.
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