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 anenomies 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.Contribution to the BUFUS Newsletter, Field excursion to Milne Bay Province - Papua New Guinea, Madl and Yip 2000

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.

The two subclasses are divided into a number of orders, those which are extinct are marked with †.

• Subclass Alcyonaria (= Octocorallia - 8 way symmetry)
  • Alcyonacea (soft corals)
  • Gorgonacea (sea fans, sea feathers)
  • Helioporacea
  • Pennatulacea (sea pens, sea pansies)
  • Stolonifera
  • Telestacea
• Subclass Zoantharia (= Hexacorallia - 6 way symmetry)
  • Ceriantharia (tube-dwelling anemones)
  • Actiniaria (sea anemones)
  • Corallimorpharia
  • Numidiaphyllida †
  • Scleractinia (stony corals)
  • Kilbuchophyllida †
  • Antipatharia (black corals, thorny corals)
  • Zoanthidea
  • Heterocorallida †
  • Rugosa †
  • Heliolitida †
  • Tabulata †
  • Cothoniida †
  • Tabuloconida †
  • Ptychodactiaria

References