NEmatocyst

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Cnidarians are a phylum of aquatic organisms that include jellyfish, corals, hydroids, and anemones. They are an ancient group of animals that are thought to have emerged more that 500 million years ago. They are characterized by their radial symmetry, their diploblastic bodies, and specialized cells called cnidocytes. Cnidarians are represented as either polyps or medusae. Sea anemones and corals are consistently found as polyps, and jellyfish have a polyp stage early in their development. These polyps are mostly sessile, but some have the ability to relocate themselves if necessary. When jellyfish mature they are medusae with a fully formed bell. When in the medusae stage jellyfish are completely mobile. Both of these forms are radially symmetrical. Both are also diploblastic, which means they only have two cell layers. The outer layer is called the ectoderm, and the inner layer is called the endoderm. They are connected by a non-cellular mass called the mesoglea, which is a jelly like substance made of water and various proteins. This mesoglea is what give structural support to the cnidarian body. The trait that most cnidarians are known for are their stinging cells, which are found in all cnidarians.

Cnidocytes, or cnidae, are cellular organelles that are enclosed by the membrane of the ectoderm. They consist of a capsule with a eversible tubule inside.They come in many forms, but the main three types nematocyst, spirocyst, and ptychocysts. Nematocysts are the most common cnidae, and are characterized by their ability to peirce other tissue. They do this with a combination of a stylus and a tubule, which then will inject some sort of venom. All nematocysts are described by their structure and function, instead of phylogeneti...

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...rane configurations, and release mediators of inflammation. Most venoms affect the muscle or nervous system, but most human reactions to jellyfish stings are consistent and the severity varies more. (Bailey, 2003) Sponges and Hydroids usually have the mildest venom among cnidarian, with the exception of some species. They usually only result in slight inflammation. Some species of jellyfish will also give a slight sting that causes inflammation. The most severe stings are caused by the Physalia species, scyphozoans, and cubozoans. (Bailey, 2003) These can give stings that cause loss of consciousness, edemas, muscle spasm, heart failure, coma, or death. (Bailey, 2003) This is just a very short list of the symptoms from cnidarian stings. This quick, and effective, firing system combined with potent venom makes many cnidarians the most venomous organisms known to man.

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