Animal Diversity Web: Cnidaria - Corals, Sea Anemones, Jellyfish, and Relatives

The Phylum Cnidaria includes such diverse forms as jellyfish, hydra, sea anemones, and corals. Cnidarians are radially or biradially symmetric, a general type of symmetry believed primitive for eumetazoans. They have achieved the tissue level of organization, in which some similar cells are associated into groups or aggregations called tissues, but true organs do not occur. Cnidarian bodies have two or sometimes three layers. A gastrovascular cavity (coelenteron) has a single exterior opening that serves as both mouth and anus. Often tentacles surround the opening. Some cells are organized into two simple nerve nets, one epidermal and the other gastrodermal, that help coordinate muscular and sensory functions.

Publisher - University of Michigan

Subjects - Cnidaria

http://animaldiversity.ummz.umich.edu/accounts/Cnidaria/

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Citation: Myers P. 2001. Animal Diversity Web: Cnidaria - Corals, Sea Anemones, Jellyfish, and Relatives. Ann Arbor, MI: University of Michigan. http://animaldiversity.ummz.umich.edu/accounts/Cnidaria/