Anthozoa

Anthozoa are a class in the phylum Cnidaria. It includes the sea anemones and the corals. It is a monophyletic clade, one of two in the Cnidaria. The other is the Medusozoa.Daly M. et al 2007. The phylum Cnidaria: a review of phylogenetic patterns and diversity 300 years after Linnaeus. Zootaxa, 1668: 127–182, Wellington.   Abstract - PDF

The class does not have a medusa larval stage in its development, unlike the rest of the phylum. Like all Cnidaria, their food-catching and defense are done by nematocysts, which are extremely effective stinging cells. Over 6,100 species have been described.estimates of species numbers differ between authorities.

There are three subclasses:

Ceriantharia: the tube-dwelling anemones or cerianthids
Hexacorallia: 4,300 species of colonial polyps, usually with 6-fold symmetry. This includes all of the stony corals, which are vital for coral reef formation, and all sea anemones, and zoanthids. 
Octocorallia: 3,000 species of colonial polyps with 8-fold symmetry. It includes the blue coral, soft corals, sea pens, and gorgonians (sea fans and sea whips).

 References 

Category:Cnidarians