Paper Summary:

This paper provides insight into the origins and biology of creatures of the phylum Cnidarian, which consists of several groups that are divided into six categories - Anthozoa (corals), Scyphozoa (jellyfish), Cubozoa (box jellies), Hydrozoa (medusae, siphonophores, hydroids, fire corals), Scyphozoa (true jellyfish), Staurozoa (stalked jellyfish), and Polypodiozoa (a single specie: Polypodium hydriforme Ussow, 1885 - a parasite). The paper discusses the evolution, modern forms, and probable future of this phylum, explaining that although cnidarians are an extremely diverse group and would not seem to be related, all of these species are armed with stinging cells called nematocysts.
The paper concludes on a cautionary note, stating that Cnidarians have no defense against human invasion and occupation of their territories, and are a key organism of reef biology, whose death often precedes the extinction of the entire ecosystem.

Outline:
Sting of Cnidarians
Evolution of Cnidarians
Development of Modern Cnidarians
Plasticity in Cnidarians
Future of Cnidarians
Works Cited

From the Paper:

"It was once thought that cnidarians did not possess a mesoderm, which in bilaterals develops into muscle tissue. However, recent research demonstrates that cnidarians do have a thin mesoderm. It is believed that stem cells in the mesodermal layer are the primary agents in the high level of plasticity shown in cnidarians (Seiple and Schmid 585). Mesodermal differentiation supports the hypothesis that cnidarians and bilaterians share a common troploblast ancestor. This ancestor is thought to be the urtriploblast, which is a small, jelly-fish like organism (Seiple and Schmid 597). The discovery of a mesodermal layer in cnidarians further supports this hypothesis."

Sample of Sources Used:

• Elliott, Joseph K., and Richard N. Mariscal. 1997. Ontogenetic and interspecific variation in the protection of anemonefishes from sea-anemones. J. Exp. Mar. Biol. Ecol. Vol. 208: 57-72.
• Fautin, Daphne G. and Romano, Sandra L. Cnidaria. 1997. Sea anemones, corals, jellyfish, sea pens, hydra. Version 24 April 1997. Website http://tolweb.org/Cnidaria/2461/1997.04.24. in The Tree of Life Web Project, Website http://tolweb.org/. [Accessed November 10, 2008]
• Fenner, Peter J. And Hadok, John C. 2002. Fatal envenomation by jellyfish causing Irukandji syndrome. Medical Journal of Australia. 177(7). Website http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=pubmed&dopt=AbstractPlus&list_uids=12358578. [Accessed November 10, 2008]
• Finnerty JR. 2001. Cnidarians Reveal Intermediate Stages in the Evolution of Hox Clusters and Axial Complexity. American Zoologist 41(3):608-620
• Griffith K, Newberry AT. 2008. Effect of flow regime on the morphology of a colonial cnidarian. Invertebrate Biology. 127 (3): 259-264.

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