Anthozoa is a class within the phylum Cnidaria that contains the sea anemones and corals. Unlike other cnidarians, anthozoans do not have a medusa stage in their development. Instead, they release sperm and eggs that form a planula, which attaches to some substrate on which the cnidarian grows.

Some anthozoans can also reproduce asexually through budding. All cnidarian species can feed by catching prey with nematocysts, sea anemones capable of catching fish and corals catching plankton. Some of the species also harbor a type of algae, dinoflagellates called zooxanthellae, in a symbiotic relationship; the reef-building corals known as hermatypic corals rely on this symbiotic relationship particularly.

The zooxanthellae benefit from using nitrogenous waste and carbon dioxide produced by the host, and the cnidarian gains photosynthetic capability and increased calcium carbonate production in hermatypic coral. Anemonies and certain species of coral live in isolation, however, most corals form colonies of genetically identical polyps; these polyps closely resemble anemonies in structure, although are generally considerably smaller.

Photo Credit: Raimond Spekking 21. August 2004