Editing Scyphozoa

{{Short description|Class of marine cnidarians, true jellyfish}}
{{Automatic taxobox
| fossil_range = {{Fossil range | Fortunian | Recent|refs = <ref name="auto">{{cite journal|doi=10.1111/pala.12306|title=A new scyphozoan from the Cambrian Fortunian Stage of South China|journal=Palaeontology|volume=60|issue=4|pages=511–518|year=2017|last1=Liu|first1=Yunhuan|last2=Shao|first2=Tiequan|last3=Zhang|first3=Huaqiao|last4=Wang|first4=Qi|last5=Zhang|first5=Yanan|last6=Chen|first6=Cheng|last7=Liang|first7=Yongchun|last8=Xue|first8=Jiaqi|doi-access=free}}</ref>}}
| image = Cauliflour Jellyfish, Cephea cephea at Marsa Shouna, Red Sea, Egypt SCUBA.jpg
| image_caption = ''[[Cephea cephea]]''
| taxon = Scyphozoa
| authority = [[Alexander W. von Götte|Götte]], 1887
| subdivision_ranks = Subgroups
| subdivision = [[#Taxonomy|See text]].
}} 
[[File:Stranded Cambrian scyphozoans.jpg|thumb|Fossilized stranded scyphozoans on a Cambrian tidal flat at [[Blackberry Hill]], Wisconsin.]]
The '''Scyphozoa''' are an exclusively marine class of the [[phylum]] [[Cnidaria]],<ref>{{cite web|url=http://thescyphozoan.ucmerced.edu/|title=The Scyphozoan|last=Dawson|first=Michael N|access-date=2008-08-11}}</ref> referred to as the '''true [[jellyfish]]''' (or "true jellies").

The class name Scyphozoa comes from the [[Greek language|Greek]] word ''[[skyphos]]'' ({{wikt-lang|grc|σκύφος}}), denoting a kind of drinking cup and alluding to the cup shape of the organism.<ref>{{cite book |last1=Towle |first1=Albert |title=Modern biology |date=1989 |publisher=Holt, Rinehart and Winston |location=Austin, Texas |isbn=978-0030139192}}</ref>

Scyphozoans have existed from the earliest [[Cambrian]] to the present.<ref name="auto"/>

==Biology==
Most species of Scyphozoa have two life-history phases, including the planktonic [[medusa (biology)|medusa]] or [[Polyp (zoology)|polyp]] form, which is most evident in the warm summer months, and an inconspicuous, but longer-lived, bottom-dwelling polyp, which seasonally gives rise to new medusae. Most of the large, often colorful, and conspicuous jellyfish found in coastal waters throughout the world are Scyphozoa.<ref name="Kramp1961">{{cite journal|last=Kramp|first=P. L.|year=1961|title=Synopsis of the medusae of the world|journal=Journal of the Marine Biological Association of the United Kingdom|volume=40|pages=1–469|doi=10.1017/s0025315400007347}}</ref> They typically range from {{convert|2|to|40|cm|in|abbr=on|frac=2}} in diameter, but the largest species, ''[[Cyanea capillata]]'' can reach {{convert|2|m|ftin|0}} across. Scyphomedusae are found throughout the world's oceans, from the surface to great depths; no Scyphozoa occur in freshwater (or on land).

As medusae, they eat a variety of crustaceans and fish, which they capture using stinging cells called [[nematocysts]]. The nematocysts are located throughout the tentacles that radiate downward from the edge of the umbrella dome, and also cover the four or eight oral arms that hang down from the central mouth. Some species, however, are instead filter feeders, using their tentacles to strain [[plankton]] from the water.<ref name=IZ>{{cite book |author= Barnes, Robert D. |year=1982 |title= Invertebrate Zoology |publisher= Holt-Saunders International |location= Philadelphia, PA|pages= 139–149|isbn= 978-0-03-056747-6}}</ref>

==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/>

==Commercial importance==
Scyphozoa include the moon jelly ''[[Aurelia aurita]]'',<ref name="pmid17486542">{{cite journal |author=Berking S, Herrmann K |title=Compartments in Scyphozoa |journal=Int. J. Dev. Biol. |volume=51 |issue=3 |pages=221–8 |year=2007 |pmid=17486542 |doi=10.1387/ijdb.062215sb |doi-access=free }}</ref> in the order Semaeostomeae, and the enormous ''[[Nemopilema nomurai]]'', in the order Rhizostomeae, found between Japan and China and which in some years causes major fisheries disruptions.

The jellyfish fished commercially for food are Scyphomedusae in the order [[Rhizostomeae]].<ref>{{cite journal|doi=10.1023/A:1011879821323|last=Omori|first=Makoto|author2=Eiji Nakano |year=2001|title=Jellyfish fisheries in southeast Asia|journal=Hydrobiologia|volume=451|issue=1/3|pages=19–26|s2cid=6518460 }}</ref> Most rhizostome jellyfish live in warm water.<ref name="Kramp1961" />

==Taxonomy==
Although the Scyphozoa were formerly considered to include the animals now referred to as the classes [[Cubozoa]] and [[Staurozoa]], they now include just three [[Extant taxon|extant]] orders (two of which are in Discomedusae, a subclass of Scyphozoa).<ref name=Daly>Daly, Brugler, Cartwright, Collins, Dawson, Fautin, France, McFadden, Opresko, Rodriguez, Romano & Stake (2007). ''[http://www.mapress.com/zootaxa/2007f/zt01668p182.pdf The phylum Cnidaria: A review of phylogenetic patterns and diversity 300 years after Linnaeus.]'' Zootaxa 1668: 127–182</ref><ref name=WoRMS>{{WoRMS |id=135220 |title=Scyphozoa |access-date=30 July 2012}}</ref> About 200 extant species are recognized at present, but the true diversity is likely to be at least 400 species.<ref name=Daly/>

Class '''Scyphozoa'''
*Subclass [[Coronamedusae]]
:* Order [[Coronatae]]
:::* Family [[Atollidae]]
:::* Family [[Atorellidae]]
:::* Family [[Linuchidae]]
:::* Family [[Nausithoidae]]
:::* Family [[Paraphyllinidae]]
:::* Family [[Periphyllidae]]
* Subclass [[Discomedusae]]
:* Order [[Rhizostomeae]]
::* Suborder Daktyliophorae
:::* Family [[Catostylidae]]
:::* Family [[Lobonematidae]]
:::* Family [[Lychnorhizidae]]
:::* Family [[Rhizostomatidae]]
:::* Family [[Stomolophidae]]
::* Suborder Kolpophorae
:::* Family [[Cassiopeidae]]
:::* Family [[Cepheidae (jellyfish)|Cepheidae]]
:::* Family [[Mastigiidae]]
:::* Family [[Thysanostomatidae]]
:::* Family [[Versurigidae]]
:* Order [[Semaeostomeae]]
:::* Family [[Cyaneidae]]
:::* Family [[Drymonematidae]]<ref>Bayha, K. M., and M. N. Dawson (2010). ''New family of allomorphic jellyfishes, Drymonematidae (Scyphozoa, Discomedusae), emphasizes evolution in the functional morphology and trophic ecology of gelatinous zooplankton.'' [[The Biological Bulletin]] 219(3): 249–267</ref>
:::* Family [[Pelagiidae]]
:::* Family [[Phacellophoridae]]
:::* Family [[Ulmaridae]]

==References==
{{Reflist|30em}}

==External links==
{{Commons category|Scyphozoa}}
* [https://web.archive.org/web/20120219193848/http://gladstone.uoregon.edu/~ghale/pdf/scyphozoa.pdf The Classification and Distribution of the Class Scyphozoa]
* {{Cite EB1911|wstitle=Scyphomedusae|short=x}}

{{Cnidaria}}
{{Taxonbar|from=Q272388}}
{{Authority control}}

[[Category:Scyphozoa| ]]
[[Category:Medusozoa]]
[[Category:Ediacaran first appearances]]