There are over 600 species of coral that have been identified and described, but it is estimated that there may be many more species that have not yet been discovered or described. Coral species are classified into two main groups: hard coral and soft coral. Hard coral, also known as stony coral, is characterized by a hard, calcium carbonate skeleton that forms the structure of the coral reef. Soft coral, on the other hand, does not have a hard skeleton and is instead supported by a flexible, spongy tissue.
Coral reefs are found in tropical and subtropical waters around the world, and the species of coral present on a particular reef will depend on a variety of factors, including water temperature, light levels, and the availability of nutrients. Coral reefs are home to a wide variety of marine life, including fish, mollusks, and crustaceans, and are an important part of the global ocean ecosystem.