Editing Scyphozoa (section)

==Anatomy==
Scyphozoans usually display a four-part symmetry and have an internal gelatinous material called [[mesoglea]], which provides the same structural integrity as a skeleton. The mesoglea includes mobile amoeboid cells originating from the epidermis.

Scyphozoans have no durable hard parts, including no head, no skeleton, and no specialized organs for respiration or excretion.<ref>Cartwright, P., Halgedahl, S.L., Hendriks, J.R., Jarrad, R.D., Marques, A.C., Collins, A.G., and Lieberman, B.S., 2007, [http://www.plosone.org/article/info:doi%2F10.1371%2Fjournal.pone.0001121 Exceptionally preserved jellyfishes from the Middle Cambrian]. PLOSONE Issue 10: e1121, p.1-7.</ref><ref>Richards, H.G., 1947, Preservation of fossil jellyfish: Bulletin of the Geological Society of America, v. 58, p. 1221.</ref> Marine jellyfish can consist of as much as 98% water, so are rarely found in fossil form.

Unlike the [[hydrozoan]] jellyfish, Hydromedusae, Scyphomedusae lack a vellum, which is a circular membrane beneath the umbrella that helps propel the (usually smaller) Hydromedusae through the water. However, a ring of muscle fibres is present within the mesoglea around the rim of the dome, and the jellyfish swims by alternately contracting and relaxing these muscles.<ref>Morris, M., and Fautin, D., 2001, Animal Diversity Web: University of Michigan Museum of Zoology, "[http://animaldiversity.ummz.umich.edu/site/accounts/information/Scyphozoa.html Scyphozoa]., Accessed: September 28, 2008.</ref>  The periodic contracting and relaxing propels the jellyfish through the water, allowing it to escape predation or catch its prey.

The mouth opens into a central stomach, from which four interconnected [[diverticulum|diverticula]] radiate outwards. In many species, this is further elaborated by a system of radial canals, with or without an additional ring canal towards the edge of the dome. Some genera, such as ''[[Cassiopea]]'', even have additional, smaller mouths in the oral arms. The lining of the digestive system includes further stinging nematocysts, along with cells that secrete [[digestive enzyme]]s.<ref name=IZ/>

The nervous system usually consists of a distributed net of cells, although some species possess more organised nerve rings. In species lacking nerve rings, the nerve cells are instead concentrated into small structures called ''[[rhopalia]]''. There are between four and sixteen of these small lobes arranged around the rim of the umbrella, where they coordinate the muscular action allowing the animal to move. Each rhopalium is typically associated with a pair of sensory pits, a [[statocyst]], and sometimes a pigment-cup [[ocellus]].<ref name=IZ/>

===Reproduction===
[[File:Schleiden-meduse-2.jpg|thumb|right|The developmental stages of [[scyphozoan]] jellyfish's life cycle:<br>'''1–3''' Larva searches for site<br>'''4–8''' Polyp grows<br>'''9–11''' Polyp [[strobilation|strobilates]]<br>'''12–14''' Medusa grows|alt=Illustration of two life stages of seven jelly species]]
Most species appear to be [[gonochorists]], with separate male and female individuals. The [[gonad]]s are located in the stomach lining, and the mature [[gamete]]s are expelled through the mouth. After fertilization, some species brood their young in pouches on the oral arms, but they are more commonly planktonic.<ref name=IZ/>

===Growth and development===
The fertilized egg produces a [[planula]]r larva which, in most species, quickly attaches itself to the sea bottom. The larva develops into the hydroid stage of the lifecycle, a tiny sessile polyp called a scyphistoma. The scyphistoma reproduces asexually, producing similar polyps by budding, and then either transforming into a medusa, or budding several medusae off from its upper surface via a process called [[strobilation]]. The medusae are initially microscopic and may take years to reach sexual maturity.<ref name=IZ/>