Coelenterata
From Wikipedia, the free encyclopedia
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| Image:Comb jellies-mba.jpg Comb jellies (Beroe spp.)
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Coelenterata is an obsolete yet common term encompassing two animal phyla, the Ctenophora (comb jellies) and the Cnidaria (coral animals, true jellies, sea anemones, sea pens, and their allies). The taxon name comes from the Greek "koilos" ("hollow"), referring to the hollow body cavity common to these two phyla. They have very simple tissue organisation, with only two layers of cells, external and internal.
[edit] History of classification
The term coelenterate is no longer recognized as scientifically valid, as the Cnidaria and Ctenophora have placed at equal rank under the Metazoa with the other phyla of animals.<ref>Excerpt from Britannica article regarding Ctenophore classification </ref> A single term encompassing these two phyla but leaving out all others of equal rank would be considered polyphyletic. Nonetheless, the term coelenterate is still used in informal settings to refer to the Cnidaria and Ctenophora.
Complicating the issue is the 1997 work of Lynn Margulis (revising an earlier model by Thomas Cavalier-Smith) that placed the Cnidaria and Ctenophora alone under the Radiata branch of the Eumetazoa subregnum<ref>Margulis, Lynn and Karlene V. Schwartz, 1997, Five Kingdoms: An Illustrated Guide to the Phyla of Life on Earth, W.H. Freeman & Company, ISBN 0613923383</ref>. (The latter refers to all the animals except the sponges, Trichoplax, and the still poorly-understood Mesozoa.) Neither grouping is accepted univerally<ref>NCBI Taxonomy Browser</ref>; however, both are commonly encountered in taxonomic literature.
[edit] References
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