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Jamfish are better.
:''This article is about the jellyfish, the sea creatures. For the pop band, see [[Jellyfish (band)]].''
{{Taxobox
| color = pink
| name = Jellyfish
| image = Jelly_Monterey.jpg
| image_width = 200px
| image_caption = [[Sea nettle]], ''Chrysaora quinquecirrha''
| regnum = [[Animal]]ia
| phylum = [[Cnidaria]]
| classis = '''Scyphozoa'''
| classis_authority = Goette, 1887
| subdivision_ranks = [[Order (biology)|Orders]]
| subdivision =
[[Stauromedusae]]<br/>
[[Coronatae]]<br/>
[[Semaeostomeae]]<br/>
[[Rhizostomae]]
}}
'''Jellyfish''' are marine invertebrates belonging to the ''Scyphozoa'' [[class (biology)|class]], and in turn the [[Phylum (biology)|phylum]] ''[[Cnidaria]]''. The body of an adult jellyfish is composed of a bell-shaped, jellylike substance enclosing its internal structure, from which the creature's [[tentacle]]s suspend. Each tentacle is covered with stinging cells ([[cnidocytes]]) that can stun or kill other animals: most jellyfish use them to secure prey or as a defense mechanism. Others, such as [[Rhizostomae]], do not have tentacles at all.
To compensate for its lack of basic sensory organs and a [[brain]], the jellyfish exploits its [[nervous system]] and [[rhopalia]] to perceive stimuli, such as light or odor, and orchestrate expedient responses. In its adult form, it is composed of 94-98% water and can be found in every [[ocean|pelagic]] area of the world.
Most jellyfish are passive drifters that feed on small fish and [[zooplankton]] that become caught in their tentacles. Jellyfish have an incomplete [[digestive system]], meaning that the same orifice is used for both food intake and waste expulsion. They are made up of a layer of [[epidermis]], [[gastrodermis]], and a thick jellylike layer called [[mesoglea]] that separates the epidermis from the gastrodermis.
Since jellyfish do not biologically qualify as actual "[[fish]]", the term "jellyfish" is considered a [[misnomer]] by some, who instead employ the names "'''jellies'''" or "'''sea jellies'''". The name "jellyfish" is also often used to denote either [[Hydrozoa]] or the box jellyfish, [[Cubozoa]].
==Life cycle and reproduction==
{{ImageStackRight|200|
[[Image:Scyphoillustration.jpg|thumb|A typical scyphomedusa jellyfish]]
[[Image:Schleiden-meduse.jpg|thumb|The developmental stages of jellyfish.]]
[[Image:Jellyfish-monterey-2003-08.jpg|thumb|Jellyfish at [[Monterey Bay Aquarium]]]]
[[Image:Tiny Jelly.jpg|thumb|Tiny jellyfish]]
[[Image:Chrysaora jelly.jpg|thumb|Chrysaora jellyfish]]
[[Image:Flower hat jellyfishes.jpg|thumb|[[Flower hat jelly]]]]
[[Image:Transparent_jellyfish_in_aquarium.jpg |thumb|[[Moon Jelly|Moon Jellies]] on display in an aquarium.]]
[[Image:Jelly cc6.jpg|thumb|A smack of jellyfish in an aquarium.]]
[[Image:Jelly cc11.jpg|thumb|The Sea nettle.]]
}}
Most jellyfish pass through two different body forms during their [[life cycle]]. The first is the ''[[polyp]]'' stage; in this phase, the jellyfish takes the form of either a [[sessile]] stalk which catches passing food, or a similar free-floating configuration. The polyp's mouth and tentacles are located [[anatomical terms of ___location|anteriorly]], facing upwards.
In the second stage, the jellyfish is known as a ''[[medusa (biology)|medusa]].'' Medusae have a [[symmetry (biology)#Radial symmetry|radially symmetric]], umbrella-shaped shaped body called a ''bell''. The medusa's tentacles hang from the border of the bell. This is the form most people know jellyfish as.
Jellyfish are [[Plant sexuality#Terminology|dioeciou]]s (that is, they are either male or female). In most cases, to reproduce, a male releases his [[sperm]] into the surrounding water. The sperm then swims into the mouth of the female jelly, allowing the fertilization of the [[ovum|ova]] process to begin. Moon jellies, however, use a different process: their eggs become lodged in pits on the oral arms, which form a temporary brood chamber to accommodate fertilization.
After fertilization and initial growth, a larval form, called the [[planula]], develops from the egg. The planula larva is small and covered with [[cilium|cilia]]. It settles onto a firm surface and develops into a [[polyp]]. The polyp is cup-shaped with tentacles surrounding a single orifices, perhaps resembling a tiny [[sea anemone]]. Once the polyp begins reproducing asexually by [[budding]], it's called a ''segmenting polyp'', or a [[scyphistoma]]. New scyphistomae may be produced by budding or new, immature jellies called [[ephyra]] may be formed. Many jellyfish can bud off new medusae directly from the medusan stage.
==Defense and feeding mechanisms==
Most jellyfish have tentacles or oral arms coated with thousands of microscopic [[nematocyst]]s; generally, each of these nematocyst has a "trigger" (cnidocil) paired with a capsule containing a coiled stinging filament, as well as barbs on the exterior. Upon contact, the filament will swifly unwind, launch into the target, and inject toxins. It can then pull the victim into its mouth, if appropriate.
Although most jellyfish are not perniciously dangerous to humans, a few are highly toxic, such as ''[[Cyanea capillata]].'' The recently discovered ''[[Carukia barnesi]]'' is also suspected of causing two deaths in Australia. Contrary to popular belief, the menacingly infamous [[Portuguese Man o' War]] (''Physalia'') is not actually a jellyfish, but a colony of [[hydrozoan polyps]].
==Body systems==
The jellyfish can detect the touch of other animals using a nervous system called a "[[nerve net]]", which is located in its [[epidermis]]. Impulses to these nerve cells are sent from nerve rings that have collected information from the environment of the jellyfish through the [[rhopalial lappet]], which is located around the animal's body. Jellyfish also have [[ocellus|ocelli]] that cannot form images, but are sensitive to light; the jellyfish can use these to determine up from down, basing its judgement on sunlight shining on the surface of the water.
Jellyfish do not have a specialized [[digestive system]], osmoregulatory system, [[central nervous system]], [[respiratory system]], or [[circulatory system]]. They are able to digest with the help of the [[gastrodermis]] that lines the [[gastrovascular cavity]], where nutrients from their food is absorbed. They do not need a respiratory system since their skin is thin enough that oxygen can easily diffuse in and out of their bodies. Jellyfish have limited control over their movement and mostly free-float, but can use a [[hydrostatic skeleton]] that controls the water pouch in their body to actuate vertical movement.
==Blooms and grouping==
A group of jellyfish is often called a "smack." Many species of jellyfish are also capable of congregating into large [[swarm]]s or "blooms" consisting of hundreds or even thousands of individuals. The formation of these blooms is a complex process that depends on [[ocean current]]s, [[nutrient]]s, temperature and oxygen content. Jellyfish will sometimes mass breed during blooms, thereby causing large booms in jellyfish population and reportedly raising major [[marine biology|ecological]] concern for a possible jellyfish outbreak.
According to Claudia Mills of the [[University of Washington]], the frequency of these blooms may be attributed to mankind's impact on marine life; she says that the breeding jellyfish may merely be taking the place of already [[overfishing|overfished]] creatures. Jellyfish researcher Marsh Youngbluth further clarifies that "jellyfish feed on the same kinds of prey as adult and young fishes, so if fish are removed from the equation, jellyfish are likely to move in."
Increased nutrient in the water, ascribed to agricultural [[Runoff (water)|runoff]], has also been cited as an antecedent to the recent proliferation of jellyfish numbers: scientist Monty Graham says, "ecosystems in which there are high levels of nutrient ... provide nourishment for the small organisms on which jellyfish feed. In waters where there is [[eutrophication]], low oxygen levels often result, favoring jellyfish as they thrive in less oxygen-rich water than fish can tolerate. The fact that jellyfish are increasing is a symptom of something happening in the ecosystem."
Areas already majorly affected by jellyfish blooms include the northern [[Gulf of Mexico]], where "moon jellies have formed a kind of gelatinous net that stretches from end to end across the gulf," and the [[Adriatic Sea]].<sup>[http://www.eurocbc.org/page727.html]</sup>
==Jellyfish in captivity==
Jellyfish are commonly displayed in a aquaria across the United States and in other countries; among the more known are the [[Monterey Bay Aquarium]], [[Vancouver Aquarium]], and [[Maui Ocean Center]]. Often the tank's background is blue with the animals illuminated by side lighting to produce a high contrast effect. In natural conditions, many of the jellies are so transparent that they can be almost impossible to see.
Holding jellies in captivity also presents other problems: for one, they are not adapted to closed spaces or areas with walls, which aquaria by definition have. They also depend on the natural currents of the ocean to transport them from place to place. To compensate for this, most professional exhibits feature water flow patterns. The Monteray Bay Aquarium uses a modified version of the "kreisel" (German for "spinning top") for this purpose.
==Cuisine==
Chilled jellyfish arm (often known as sesame jellyfish or jellyfish salad) is a common type of appetizer in the [[Shanghai cuisine|Shanghai-style Chinese cuisine]], which is often served with [[sesame|sesame seeds]], [[sesame oil]] and, ocassionally, [[spring onion]]. A similar dish appears in [[Vietnamese cuisine|Vietnam]], with [[red chilli pepper]] added.
==Treatment of stings==
When stung by a jellyfish, [[first aid]] may be in order. Though most jellyfish stings are not deadly, other stings, such as those perpetrated by the [[Cubozoa|box jellyfish]] (''[[Chironex fleckeri]]'') — the most venomous marine creature and possibly the most venomous of any creature on earth — may be fatal. Serious stings may cause [[anaphylaxis]] and eventual paralyzation, and hence people stung by jellyfish must get out of the water to avoid drowning. In these serious cases, advanced professional care must be sought. This care may include administration of an [[antivenin]] and other supportive care such as required to treat the symptoms of [[anaphylactic shock]].
There are three goals of first aid for uncomplicated jellyfish stings: prevent injury to rescuers, inactivate the [[nematocysts]], and remove any tentacles stuck on the patient. To prevent injury to rescuers, barrier clothing should be worn. This protection may include anything from panty hose to wet suits to full-body sting-proof suits. Inactivating the [[nematocysts]], or stinging cells, prevents further injection of [[venom (poison)|venom]] into the patient. Five percent [[acetic acid]] solution (white vinegar) is the preferred method, although meat tenderizer, or [[sodium bicarbonate]] ([[baking soda]]) will neutralize any nematocysts that have not yet discharged into the skin. Meat tenderizer should not be left on the skin for more than 15 minutes, and none of these substances should be used in the eyes. In the case of stings on or around the eyes, the solution may be placed on a towel and dabbed ''around'' the eyes, but not in them. Salt water may also be used in case any of these compounds are not readily available, but fresh water should never be used. Rinsing the sting site with fresh water, rubbing the wound, or using alcohol, spirits, ammonia, or urine will encourage the release of venom.
Once deactivated, the stinging cells must be removed. This can be accomplished by picking off tentacles left on the body. First aid providers should be careful to use gloves or another readily available barrier device to prevent personal injury, and to follow standard [[universal precautions]]. After large pieces of the jellyfish are removed, shaving cream may be applied to the area and a knife edge, safety razor, or credit card may be used to take away any remaining [[nematocysts]].
Beyond initial first aid, [[antihistamines]] such as [[diphenhydramine]] ([[Benadryl]]) may be used to control skin irritation ([[pruritis]]).
==See also==
{{commons|Jellyfish}}
*[[Sea nettle]]
*[[Moon Jelly]]
*[[Cubozoa]] (the box jellyfish)
*[[Physconect siphonophore]]
*[[Cassiopea]]s
*[[Cotylorrhiza tuberculata]] (also called ''Fried Egg Jellyfish'').
*[[Rhizostoma pulmo]] (also known as the ''Rhizostoma octopus'' or ''White Jellyfish'').
==External links==
*[http://water.dnr.state.sc.us/marine/pub/seascience/jellyfi.html Sea Science: Jellyfish]
*[http://www.malawicichlidhomepage.com/other/cotylorhiza_tuberculata.html Cotylorhiza tuberculata]
*[http://www.vattenkikaren.gu.se/fakta/arter/cnidaria/scyphozo/rhizocto/rhizocne.html Rhizostoma pulmo]
*[http://www.aquaticcommunity.com/universal-id43.html Jellyfish information]
*[http://jellieszone.com/captivejellies.htm Keeping Jellies in an Aquarium]
*[http://www.emedicine.com/emerg/topic104.htm Treatment of Coelenterate and Jellyfish Envenomations]
[[Category:Cnidarians]]
{{Link FA|pt}}
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