Scleractinia, also called stony corals, are marine corals that generate a hard skeleton. They first appeared in the Middle Triassic and descended from the tabulate and rugose corals that barely survived the end of the Permian. Much of the framework of modern coral reefs is formed by scleractinians. Stony corals numbers are expected to decline due to the effects of global warming.
There are two groups of Scleractinia:
- Compound corals live in colonies in clear, oligotrophic, shallow tropical waters; they are the world's primary reef-builders.
- Solitary corals are found in all regions of the oceans and do not build reefs. In addition to living in tropical waters some solitary corals live in temperate, polar waters, or below the photic zone down to 6,000 m (20,000 ft)