Cnidaria

Cnidaria
East Coast sea nettle Chrysaora quinquecirrha (?)
Scientific classification
Kingdom:	Animalia
(unranked):	Radiata
Phylum:	Cnidaria
Subphylum:	Medusozoa

Cnidaria is a phylum with about 11,000 species of animals.^[1] All of them are simple and aquatic, and most of them live in the sea. Some are colonial, composed of zooids which may be clones. Cnidarian zooids may take the form of polyps or medusae at different phases of their life.

Cnidaria take their name from special cells which have organelles that sting: the nematocysts. This device is largely responsible for their success: it is their main specialised and distinctive cell type.^[2]

1. ↑ Daly M. et al 2007. The phylum Cnidaria: a review of phylogenetic patterns and diversity 300 years after Linnaeus. Zootaxa, 1668: 127–182, Wellington. [1]
2. ↑ Ruppert E.E; Fox R.S. & Barnes R.D. 2004. Invertebrate Zoology. Brooks/Cole 7th ed. ISBN 978-0-03-025982-1