Scleractinia

Scleractinia, commonly known as stony corals, is an order of corals within the class Anthozoa and the subclass Hexacorallia. They secrete hard calcium carbonate skeletons and are a principal source of coral reefs, although not all species contribute to reef construction. The skeleton is composed of aragonite, produced by cells on the outer body surface.

Most scleractinians are colonial, though some are solitary. Individual animals are called polyps, housed in cup-like corallites that are part of the shared skeleton. The skeleton bears internal structures such as septa and costae. The typical polyp bears tentacles in groups of six, with variations in some species. Growth occurs by budding at the polyp margins.

Many species host symbiotic photosynthetic dinoflagellates (zooxanthellae) within their tissues, providing energy through photosynthesis and supporting rapid reef growth in shallow, sunlit waters. Other species are azooxanthellate and feed primarily on plankton and detritus.

Reproduction occurs sexually through broadcast spawning or brooding, releasing eggs and sperm or developing planula larvae. Asexual reproduction by budding and fragmentation helps colonies expand and recover after disturbance.

Scleractinia inhabit warm, clear, shallow marine environments in tropical and subtropical regions. Hermatypic (reef-building) species contribute to the framework of coral reefs, while ahermatypic species do not form large reefs and can occur in deeper or cooler waters.

They face threats from climate change, including bleaching due to elevated sea temperatures, and ocean acidification that reduces calcification. Other pressures include disease, pollution, overfishing, and habitat destruction. Conservation relies on reef protection, restoration, and sustainable management.