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Scleractinia, also called stony star corals, are exclusively marine animals; they are very similar to sea anemones but generate a hard skeleton. They first appeared in the Middle Triassic and replaced tabulate and rugose corals that went extinct at the end of the Permian.
There are two groups of Scleractinia:
- colonial corals found in clear, shallow tropical waters; they are the world's primary reef-builders.
- solitary corals that are found in all regions of the oceans and that do no build reefs. Some lives in temperate, polar waters, or below the photic zone down to 6000 meters.
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