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More than 6000 anthozoan species exist today, making up about two thirds of the extant diversity in the phylum Cnidaria. Most modern forms rely on a symbiotic relationship with zooxanthellae, dinoflagellate algae of the genus Symbiodinium. The relationship appears to be mutualistic, with the zooxanthellae taking up waste and carbon dioxide from their hosts, giving carbohydrates and oxygen in return. It is the zooxanthellae that give corals and anemones their colour; when ocean conditions become such that the zooxanthellae can no longer survive, it is their absence that causes coral bleaching and the decline of reefs.
Scleractinia, or stony corals (e.g. brain coral), are amongst the most important hermatypic (reef-building) organisms today. However, modern anthozoans show a wide range of morphology and occupy a numerous different ecological niches. The pictures below give an indication of their diversity (click on a thumbnail to enlarge, then click the back button in your browser to return).
 A sea anemone, subclass Zoantharia, order Actiniaria |
 Brain coral, a scleractinian coral, subclass Zoantharia |
 A sea fan, subclass Alcyonaria, order Gorgonacea |
 A sea pen, subclass Alcyonaria, order Pennatulacea |  A zoanthid soft coral, subclass Zoantharia, order Zoanthidae |
Author: Ben Kotrc
Last updated: 21 November 2005
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