Anthozoa

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 be 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 harbour 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 by using nitrogenous waste and carbon dioxide produced by the host, and the cnidarian gains photosynthetic capability and increased calcium carbonate production in hermatypic corals.

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. Most kinds of stony coral live in all parts of the underwater world.



Phylogeny
The two subclasses are divided into a number of orders and a series of orders. , extinct orders from the Paleozoic (570-245 m.y.a.) are marked with †.
 * Subclass Alcyonaria (= Octocorallia) (8-way symmetry)
 * Alcyonacea (soft corals)
 * Gorgonacea (sea fans, sea feathers)
 * Helioporacea (= Coenothecalia) (Indo-Pacific blue coral)
 * Pennatulacea (sea pens, sea pansies)
 * Stolonifera (organ-pipe coral, tree fern coral)
 * Telestacea (soft corals)
 * Subclass Zoantharia (= Hexacorallia (6-way symmetry)
 * Ceriantharia (tube-dwelling anemones)
 * Actiniaria (sea anemones)
 * Corallimorpharia
 * Numidiaphyllida †
 * Scleractinia (= Madreporaria) (stony corals)
 * Kilbuchophyllida †
 * Antipatharia (black corals, thorny corals)
 * Zoanthidea
 * Heterocorallia †
 * Rugosa † (= Tetracoralla) (horned corals)
 * Heliolitida †
 * Tabulata † (tabulate corals)
 * Cothoniida †
 * Tabuloconida †
 * Ptychodactiaria