jellyfish

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JellyfishTemporal range: 505–0Ma

Cambrian – Recent

Pacific sea nettle

Chrysaora fuscescens

Scientific classification

Kingdom: Animalia

Phylum: Cnidaria

Subphylum: MedusozoaPetersen, 1979

Classes

CubozoaHydrozoaPolypodiozoaScyphozoaStaurozoa

JellyfishFrom Wikipedia, the free encyclopedia

Jellyfish or jellies are the major non-polyp form of individuals of thephylum Cnidaria. They are typified as free-swimming marine animalsconsisting of a gelatinous umbrella-shaped bell and trailing tentacles.The bell can pulsate for locomotion, while stinging tentacles can be usedto capture prey.

Jellyfish are found in every ocean, from the surface to the deep sea. Afew jellyfish inhabit freshwater. Large, often colorful, jellyfish arecommon in coastal zones worldwide. Jellyfish have roamed the seas forat least 500 million years,[1] and possibly 700 million years or more,making them the oldest multi-organ animal.[2]

Contents1 Terminology2 Anatomy

2.1 Nervous system2.2 Vision2.3 Size

3 Classification and evolution4 Life-cycle

4.1 Reproduction4.2 Lifespan

5 Ecology5.1 Feeding5.2 Predation5.3 Blooms5.4 Population5.5 Habitats

6 Relationship to humans6.1 Culinary6.2 Fisheries6.3 Biotechnology6.4 Aquaria6.5 Toxicity6.6 Treatment6.7 Hazards6.8 References in media

7 Taxonomy8 Haeckel's medusae

PreЄ Є O S D C P T J K Pg N

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Flower hat jelly, Olindias formosa,photographed at the Osaka AquariumKaiyukan

A purple-striped jelly at the MontereyBay Aquarium

A moon jelly shown in false color atthe Pairi Daiza

9 See also10 References11 External links

TerminologyThe term medusa was coined by Linnaeus in 1752, alluding to thetentacled head of Medusa in Greek mythology.[3] This term refersexclusively to the non-polyp life-stage which occurs in many cnidarians,which is typified by a large pulsating gelatinous bell with long trailingtentacles. All medusa-producing species belong to the sub-phylumMedusozoa.

The English popular name jellyfish has been in use since 1796.[3] It hastraditionally also been applied to other animals sharing a superficialresemblance, for example ctenophores (members from another phylumof common, gelatinous and generally transparent or translucent, free-swimming planktonic carnivores now known as comb jellies) wereincluded as "jellyfishes".[4] Even some scientists include the phylumctenophora when they are referring to jellyfish.[5] Other scientists preferto use the more all-encompassing term gelatinous zooplankton, whenreferring to these, together with other soft-bodied animals in the watercolumn.[6]

As jellyfish are not vertebrates, let alone true fish, the word jellyfish isconsidered by some to be a misnomer. Public aquariums may use theterms jellies or sea jellies instead.[7] Some sources may use the term"jelly" to refer to organisms in this taxon, as "jellyfish" may beconsidered inappropriate.[8]

Many textbooks and sources refer to only scyphozoa as "truejellyfish".[9][10]

A group of jellyfish is sometimes called a bloom or a swarm.[11]

"Bloom" is usually used for a large group of jellyfish that gather in asmall area, but may also have a time component, referring to seasonalincreases, or numbers beyond what was expected.[12] Another collectivename for a group of jellyfish is a smack,[13] although this term is notcommonly used by scientists who study jellyfish. Jellyfish are "bloomy"by nature of their life cycles, being produced by their benthic polypsusually in the spring when sunshine and plankton increase, so theyappear rather suddenly and often in large numbers, even when an

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A white-spotted jellyfish off the northcoast of Haiti

The major surfaces and axes of ajellyfish

ecosystem is in balance.[14] Using "swarm" usually implies some kind ofactive ability to stay together, which a few species such as Aurelia, themoon jelly, demonstrate.[15]

Medusa jellyfish may be classified as scyphomedusae ("true" jellyfish),stauromedusae (stalked jellyfish), cubomedusae (box jellyfish), orhydromedusae, according to which clade their species belongs.[16]

In biology, a medusa (plural: medusae) is a form of cnidarian in whichthe body is shaped like an umbrella, in contrast with polyps. Medusaevary from bell-shaped to the shape of a thin disk, scarcely convex aboveand only slightly concave below. The upper or aboral surface is calledthe exumbrella and the lower surface is called the subumbrella; themouth is located on the lower surface, which may be partially closed by a membrane extending inward from themargin (called the velum). The digestive cavity consists of the gastrovascular cavity and radiating canals whichextend toward the margin; these canals may be simple or branching, and vary in number from few to many. Themargin of the disk bears sensory organs and tentacles as its said.

German biologist Ernst Haeckel popularized medusae through his vivid illustrations, particularly inKunstformen der Natur.

AnatomyMost jellyfish do not have specialized digestive, osmoregulatory, centralnervous, respiratory, or circulatory systems. The manubrium is a stalk-like structure hanging down from the centre of the underside, with themouth at its tip. This opens into the gastrovascular cavity, wheredigestion takes place and nutrients are absorbed. It is joined to the radialcanals which extend to the margin of the bell.[17] Jellyfish do not need arespiratory system since their skin is thin enough that the body isoxygenated by diffusion. They have limited control over movement, butcan use their hydrostatic skeleton to navigate through contraction-pulsations of the bell-like body; some species actively swim most of thetime, while others are mostly passive.[citation needed] The body iscomposed of over 95% water; most of the umbrella mass is a gelatinousmaterial — the jelly — called mesoglea which is surrounded by twolayers of protective skin. The top layer is called the epidermis, and the inner layer is referred to as gastrodermis,which lines the gut.

Nervous system

Jellyfish employ a loose network of nerves, located in the epidermis, which is called a "nerve net".[18] Althoughtraditionally thought not to have a central nervous system, nerve net concentration and ganglion-like structures

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could be considered to constitute one in most species.[19] A jellyfish detects various stimuli including the touchof other animals via this nerve net, which then transmits impulses both throughout the nerve net and around acircular nerve ring, through the rhopalial lappet, located at the rim of the jellyfish body, to other nerve cells.

Another counter to the "brainless jellyfish" hypothesis is that some species explicitly adapt to tidal flux tocontrol their location. In Roscoe Bay, jellyfish ride the current at ebb tide until they hit a gravel bar, and thendescend below the current. They remain in still waters waiting for the tide to rise, ascending and allowing it tosweep them back into the bay. They monitor salinity to avoid fresh water from mountain snowmelt, again bydiving until they find enough salt.[2]

Vision

Some jellyfish have ocelli: light-sensitive organs that do not form images but which can detect light, and areused to determine up from down, responding to sunlight shining on the water's surface. These are generallypigment spot ocelli, which have some cells (not all) pigmented.

Certain species of jellyfish, such as the box jellyfish, have been revealed to be more advanced than theircounterparts. The box jellyfish has 24 eyes, two of which are capable of seeing color, and four parallelinformation processing areas or rhopalia that act in competition,[20] supposedly making it one of the fewcreatures to have a 360-degree view of its environment.[21]

The eyes are suspended on stalks with heavy crystals on one end, acting like a gyroscope to orient the eyesskyward. They look upward to navigate from roots in mangrove swamps to the open lagoon and back, watchingfor the mangrove canopy, where they feed.[2]

Size

Jellyfish range from about one millimeter in bell height and diameter to nearly two meters in bell height anddiameter; the tentacles and mouth parts usually extend beyond this bell dimension.

The smallest jellyfish are the peculiar creeping jellyfish in the genera Staurocladia and Eleutheria, which havebell disks from 0.5 mm to a few mm diameter, with short tentacles that extend out beyond this, on which thesetiny jellyfish crawl around on seaweed or the bottoms of rocky pools.[22] Many of these tiny creeping jellyfishcannot be seen in the field without a hand lens or microscope; they can reproduce asexually by splitting in half(called fission). Other very small jellyfish, which have bells about one mm, are the hydromedusae of manyspecies that have just been released from their parent polyps;[23] some of these live only a few minutes beforeshedding their gametes in the plankton and then dying, while others will grow in the plankton for weeks ormonths. The hydromedusae Cladonema radiatum and Cladonema californicum are also very small, living formonths, yet never growing beyond a few mm in bell height and diameter.[24] Another small species of jellyfishis the Australian Irukandji, which is about the size of a fingernail.[2]

The lion's mane jellyfish, Cyanea capillata, was long-cited as the largest jellyfish, and arguably the longestanimal in the world, with fine, thread-like tentacles that may extend up to 36.5 metres (120 ft) long (thoughmost are nowhere near that large).[25][26] They have a moderately painful, but rarely fatal, sting. Claims that this

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A relative comparison of the size of aScyphozoa jellyfish with the size of ahuman being

jellyfish may be the longest animal in the world are likely exaggerated;some other planktonic cnidarians called siphonophores may typically betens of meters long and seem a more legitimate candidate for longestanimal.[citation needed]

The increasingly common giant Nomura's jellyfish, Nemopilemanomurai, found in some, but not all years in the waters of Japan, Koreaand China in summer and autumn is probably a much better candidatefor "largest jellyfish", since the largest Nomura's jellyfish in late autumncan reach 200 centimetres (79 in) in bell (body) diameter and about 200kilograms (440 lb) in weight, with average specimens frequentlyreaching 90 centimetres (35 in) in bell diameter and about 150 kilograms(330 lb) in weight.[27][28] The large bell mass of the giant Nomura'sjellyfish[29] can dwarf a diver and is nearly always much greater than theup-to-100 centimetres (39 in) bell diameter Lion's Mane.[30]

The rarely encountered deep-sea jellyfish Stygiomedusa gigantea isanother solid candidate for "largest jellyfish", with its thick, massive bellup to 100 centimetres (39 in) wide, and four thick, "strap-like" oral armsextending up to 6 metres (20 ft) in length,[31] very different from thetypical fine, threadlike tentacles that rim the umbrella of more-typical-looking jellyfish, including the Lion'sMane.

Classification and evolutionMedusa jellyfish are a life stage exhibited in some species of the phylum Cnidaria. Medusa jellyfish belongexclusively to Medusozoa, the clade of cnidarians which excludes Anthozoa (e.g., corals and anemones). Thissuggests that the medusa form evolved after the polyps.[32]

The phylogenetics of this group are complex and still being worked out. The Medusozoa appear to be a sistergroup to Octocorallia.[33] Staurozoa appears to be the earliest diverging; Cubozoa and the coronate Scyphozoaform a clade that is the sister group of Hydrozoa plus discomedusan Scyphozoa. The Hydrozoa are the sistergroup of discomedusan Scyphozoa. Limnomedusae (Trachylina) is the sister group of hydroidolinans. Thisgroup may be the earliest diverging lineage among Hydrozoa. Semaeostomeae is a paraphyletic clade withRhizostomeae.

There are four major classes of medusozoan Cnidaria:

Scyphozoa are often called true jellyfish. They have tetra-radial symmetry. They have tentacles aroundthe outer margin of the bowl-shaped bell, and oral arms around the mouth.Cubozoa (box jellyfish) have a box-shaped bell, and their velarium assists them to swim more quickly.Box jellyfish may be related more closely to "true jellyfish" than either are to hydrozoa.[32]

Hydrozoa may form medusa which resemble scyphozoans (but generally with a velum) and aredistinguished by an absence of cells in the mesoglea. However, many hydrozoa species do not form

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The lion's mane jellyfish Cyaneacapillata is one of the larger speciesof jellyfish.

A sea nettle at the Monterey BayAquarium

medusa at all (such as hydra, which is hence not considered ajellyfish).Staurozoa (stalked jellyfish) do not have a polyp stage, howeverthe medusa is generally sessile, oriented upside down and with astalk from the "bell" planted to the substrate. Until recently,staurozoa was classified within scyphozoa.

Some other animals are frequently associated with or mistaken formedusa jellyfish.

Siphonophorae are an order of hydrozoa which generally live ascolonies (for example, free-swimming chains of repeated units,some units similar to polyps or to medusa). They are notconsidered medusa jellyfish. A well-known example is thePortuguese Man o' War.Ctenophores (comb jellies) are a separate phylum from cnideria.Their method of propolsion is cillia paddles rather than a pulsatingbell.Salps are transparent, gelatinous marine organisms that formpelagic colonies like siphonophores. Salps are chordates, and assuch are actually more closely related to humans than they are tocnidarians and comb jellies.[34]

There are over 200 species of Scyphozoa, about 50 species of Staurozoa,about 20 species of Cubozoa, and in Hydrozoa there are about 1000–1500 species that produce medusa (and many more hydrozoa speciesthat do not).[35][36]

Life-cycleSee also: Biological life cycle and Developmental biology

Most jellyfish alternate between polyp and medusa generations duringtheir life cycle. Additionally, there are several possible larval life-stages.

After fertilization a primitive free-swimming larval form, called the planula, develops. The planula is a smalllarva covered with cilia. It settles onto a firm surface and develops into a polyp. Some polyps can also asexuallyproduce a creeping frustule larval form, which then also develops into a new polyp.

The polyp is generally a small planted stalk with a mouth that is ringed by upward-facing tentacles. The polypsare like miniatures of the closely related anthozoan (sea anemones and corals) polyps, which are also membersof Cnidaria. The jellyfish polyp may be sessile, living on the bottom or another substrate such as floats or boathulls, or it may be free-floating or attached to tiny bits of free-living plankton[37] or rarely, fish[38] or otherinvertebrates. Polyps may be solitary or colonial. Polyp colonies form by strobilation, resulting in multiplepolyps which share a common stomach cavity.[39] Most polyps are very small, measured in millimeters. They

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The developmental stages ofscyphozoan jellyfish's life cycle:1–3 Larva searches for site4–8 Polyp grows9–11 Polyp strobilates12–14 Medusa grows

feed continuously. The polyp stage may last for years.

Eventually the polyp gives rise to the medusa stage. New medusae are usually created asexually by strobilationor budding from the polyp. The medusa is the life stage which is most typically identified as a jellyfish.

Reproduction

Jellyfish reproduce both sexually and asexually. Upon reaching adult size, jellyfish spawn daily if there isenough food. In most species, spawning is controlled by light, so the entire population spawns at about the sametime of day, often at either dusk or dawn.[40] Jellyfish are usually either male or female (hermaphroditicspecimens are occasionally found).

In most cases, adults release sperm and eggs into the surrounding water,where the (unprotected) eggs are fertilized and mature into neworganisms. In a few species, the sperm swim into the female's mouthfertilizing the eggs within the female's body where they remain duringearly development stages. In moon jellies, the eggs lodge in pits on theoral arms, which form a temporary brood chamber for the developingplanula larvae.

After a growth interval, the polyp begins reproducing asexually bybudding and, in the Scyphozoa, is called a segmenting polyp, or ascyphistoma. New scyphistomae may be produced by budding or formnew, immature jellies called ephyrae. A few jellyfish species canproduce new medusae by budding directly from the medusan stage.Budding sites vary by species; from the tentacle bulbs, the manubrium(above the mouth), or the gonads of hydromedusae. A few species ofhydromedusae reproduce by fission (splitting in half).[37]

In the second stage, the tiny polyps asexually produce jellyfish, each ofwhich is also known as a medusa. Tiny jellyfish (usually only amillimeter or two across) swim away from the polyp and then grow andfeed in the plankton.[citation needed] Medusae have a radially symmetric,umbrella-shaped body called a bell, which is usually supplied withmarginal tentacles – fringe-like protrusions from the bell's border thatcapture prey. A few species of jellyfish do not have the polyp portion ofthe life cycle, but go from jellyfish to the next generation of jellyfishthrough direct development of fertilized eggs.[citation needed]

Most jellyfish have a second stage to their life cycle, the planula larvae phase, following the initial egg andsperm phase. Although this is a short lived stage for jellyfish, it is an important phase when the fertilized eggsthat had previously undergone embryonic development, hatch, and planulae emerge from the females mouth orbrood pouch and are off on their own.[41]

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Lifespan

Jellyfish lifespans typically range from a few hours (in the case of some very small hydromedusae) to severalmonths. Life span and maximum size varies by species. Jellyfish held in public aquariums are carefully tended,fed daily even when food might be seasonally rare in the wild, and sometimes treated with antibiotics if theydevelop infections, so may live several years, though this would be very unusual in the sea. Most large coastaljellyfish live 2 to 6 months, during which they grow from a millimeter or two to many centimeters in diameter.One unusual species is reported to live as long as 30 years[citation needed]. Another unusual species, T. nutricula,falsely reported as Turritopsis dohrnii, might be effectively immortal because of its ability under certaincircumstances in the laboratory to transform from medusa back to the polyp stage, thereby escaping the deaththat typically awaits medusae post-reproduction if they have not otherwise been eaten by some other oceanorganism .[42] So far this transdifferentian of life form has been observed only in the laboratory and it is notknown if it actually occurs in wild Turritopsis populations.

Ecology

Feeding

Jellies are carnivorous, feeding on plankton, crustaceans, fish eggs, small fish and other jellyfish, ingesting andvoiding through the same hole in the middle of the bell. Jellies hunt passively using their tentacles as drift nets.

Predation

Other species of jellyfish are among the most common and important jellyfish predators, some of whichspecialize in jellies. Other predators include tuna, shark, swordfish, sea turtles and at least one species of Pacificsalmon. Sea birds sometimes pick symbiotic crustaceans from the jellyfish bells near the sea's surface,inevitably feeding also on the jellyfish hosts of these amphipods or young crabs and shrimp.

Blooms

Jellyfish bloom formation is a complex process that depends on ocean currents, nutrients, sunshine,temperature, season, prey availability, reduced predation and oxygen concentrations. Ocean currents tend tocongregate jellyfish into large swarms or "blooms", consisting of hundreds or thousands of individuals. Bloomscan also result from unusually high populations in some years. Jellyfish are better able to survive in nutrient-rich, oxygen-poor water than competitors, and thus can feast on plankton without competition. Jellyfish mayalso benefit from saltier waters, as saltier waters contain more iodine, which is necessary for polyps to turn intojellyfish. Rising sea temperatures caused by climate change may also contribute to jellyfish blooms, becausemany species of jellyfish are relatively better able to survive in warmer waters.[44]

Scientists have little historic data about jellyfish populations.[14]

One hypothesis is that the global increase in jellyfish bloom frequency may stem from human impact. In somelocations jellyfish may be filling ecological niches formerly occupied by now overfished creatures, but this

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Aurelia sp. occurs in large quantitiesin most of the world's coastal waters.Members of this genus are nearlyidentical to each other.

Map of population trends of nativeand invasive species of jellyfish[43]

Increase (high certainty)

Increase (low certainty)

Stable/variable

Decrease

No data

hypothesis lacks supporting data.[14] Youngbluth states that "jellyfishfeed on the same kinds of prey as adult and young fish, so if fish areremoved from the equation, jellyfish are likely to move in."[45]

Some jellyfish populations that have shown clear increases in the pastfew decades are invasive species, newly arrived from other habitats:examples include the Black Sea, Caspian Sea, Baltic Sea, central andeastern Mediterranean, Hawaii, and tropical and subtropical parts of theWest Atlantic (including the Caribbean, Gulf of Mexico andBrazil).[46][47] Invasive populations can expand rapidly because theyoften face no predators in the new habitat.

Increased nutrients, ascribed to agricultural runoff, have been cited ascontributing to jellyfish proliferation. Graham states, "ecosystems inwhich there are high levels of nutrients ... provide nourishment for thesmall organisms on which jellyfish feed. In waters where there iseutrophication, low oxygen levels often result, favoring jellyfish as theythrive in less oxygen-rich water than fish can tolerate. The fact thatjellyfish are increasing is a symptom of something happening in theecosystem."[45]

Population

Jellyfish populations may be expanding globally as a result ofoverfishing and the availability of excessive nutrients due to landrunoff.[48][49] When marine ecosystems become disturbed jellyfish canproliferate. For example, jellyfish reproduce rapidly and have fastgrowth rates; they predate many species, while few species predatethem; and they feed via touch rather than visually, so they can feedeffectively at night and in turbid waters.[50][51] It may become difficultfor fish stocks to reestablish themselves in marine ecosystems once theyhave become dominated by jellyfish, because jellyfish feed on plankton, which includes fish eggs andlarvae.[52][53]

Habitats

Although most jellyfish are marine animals, some inhabit freshwater. This is most common for hydromedusae(in fact many hydrozoa inhabit freshwater). The best known example is the cosmopolitan freshwater jellyfish,Craspedacusta sowerbii. It is less than an inch (2.5 cm) in diameter, colorless and does not sting.

Some other jellyfish populations have also become restricted into lakes, such as Jellyfish Lake in Palau.

Although what first comes to mind as the common domain of jellyfish is living well up off the ocean floor inthe plankton, a few species of jellyfish are closely associated with the bottom for much of their lives (that is,

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Cannonball jellyfish, Stomolophusmeleagris, are harvested for culinarypurposes

Rehydrated jellyfish strips preparedwith soy sauce and sesame oil

they can be considered benthic). The upside-down jellyfish in the genus Cassiopea typically lie on the bottomof shallow lagoons where they sometimes pulsate gently with their umbrella top facing down. The tiny creepingjellyfish Staurocladia and Eleutheria (see section on Size, above) cannot swim and "walk" around on seaweedfronds or rocky bottoms on their tentacles. Most hydromedusae and scyphomedusae that live in coastal habitatsfind themselves on the bottom periodically, where they may stop swimming for awhile, and certain box jellyfishspecies also rest on the sea bed in shallow water.[54] Even some deep-sea species of hydromedusae andscyphomedusae are usually collected on or near the bottom. All of the stauromedusae are found attached toeither seaweed or rocky or other firm material on the bottom.[55]

Relationship to humans

Culinary

In some countries, such as Japan, jellyfish are known as a delicacy."Dried jellyfish" has become increasingly popular throughout the world.The jellyfish is dried to prevent spoiling; if not dried they can spoilwithin a matter of hours. Once dried, they can be stored for weeks at atime. Only scyphozoan jellyfish belonging to the order Rhizostomeaeare harvested for food; about 12 of the approximately 85 species. Mostof the harvest takes place in southeast Asia.[56] Rhizostomes, especiallyRhopilema esculentum in China (�� hǎizhē, "sea stings") andStomolophus meleagris (cannonball jellyfish) in the United States, arefavored because of their larger and more rigid bodies and because theirtoxins are harmless to humans.[57]

Traditional processing methods,carried out by a Jellyfish Master,involve a 20- to 40-day multi-phase procedure in which afterremoving the gonads and mucousmembranes, the umbrella and oral arms are treated with a mixture oftable salt and alum, and compressed. Processing reduces liquefaction,odor, the growth of spoilage organisms, and makes the jellyfish drier andmore acidic, producing a "crunchy and crispy texture." Jellyfishprepared this way retain 7–10% of their original weight, and theprocessed product contains approximately 94% water and 6% protein.Freshly processed jellyfish has a white, creamy color and turns yellow orbrown during prolonged storage.

In China, processed jellyfish are desalted by soaking in water overnight and eaten cooked or raw. The dish isoften served shredded with a dressing of oil, soy sauce, vinegar and sugar, or as a salad with vegetables. InJapan, cured jellyfish are rinsed, cut into strips and served with vinegar as an appetizer.[57][58] Desalted, ready-to-eat products are also available.[57]

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Global harvest of jellyfish inthousands of tonnes as reported by the

FAO[59]

The hydromedusa Aequorea victoria

Fisheries

Fisheries have begun harvesting the American cannonball jellyfish,Stomolophus meleagris, along the southern Atlantic coast of the UnitedStates and in the Gulf of Mexico for export to Asia.[57]

Jellyfish are also harvested for their collagen, which can be used for avariety of applications including the treatment of rheumatoid arthritis.

Biotechnology

In 1961, Osamu Shimomura extracted green fluorescent protein (GFP)and another bioluminescent protein, called aequorin, from the large andabundant hydromedusa Aequorea victoria, while studying photoproteinsthat cause bioluminescence in this species. Three decades later, DouglasPrasher sequenced and cloned the gene for GFP. Martin Chalfie figuredout how to use GFP as a fluorescent marker of genes inserted into othercells or organisms. Roger Tsien later chemically manipulated GFP toproduce other fluorescent colors to use as markers. In 2008, Shimomura,Chalfie and Tsien won the Nobel Prize in Chemistry for their work withGFP.

Man-made GFP became commonly used as a fluorescent tag to showwhich cells or tissues express specific genes. The genetic engineeringtechnique fuses the gene of interest to the GFP gene. The fused DNA isthen put into a cell, to generate either a cell line or (via IVF techniques)an entire animal bearing the gene. In the cell or animal, the artificialgene turns on in the same tissues and the same time as the normal gene, making GFP instead of the normalprotein. Illuminating the animal or cell reveals what tissues express that protein—or at what stage ofdevelopment. The fluorescence shows where the gene is expressed.[60]

Aquaria

Jellyfish are displayed in many public aquaria. Often the tank's background is blue and the animals areilluminated by side light, increasing the contrast between the animal and the background. In natural conditions,many jellies are so transparent that they are nearly invisible.

Jellyfish are not adapted to closed spaces. They depend on currents to transport them from place to place.Professional exhibits feature precise water flows, typically in circular tanks to avoid trapping specimens incorners. The Monterey Bay Aquarium uses a modified version of the kreisel (German for "spinning top") forthis purpose. As of 2009, jellyfish were becoming popular in home aquaria.[61][62][63][64]

Toxicity

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A group of Pacific sea nettle jellyfish,Chrysaora fuscescens, in an aquariumexhibit

Like many species of jellyfish, thesting of some species of Mastigiashave little or no discernible effect onhumans.

Jellyfish sting their prey using nematocysts, also called cnidocysts,stinging structures located in specialized cells called cnidocytes, whichare characteristic of all Cnidaria. Contact with a jellyfish tentacle cantrigger millions of nematocysts to pierce the skin and inject venom,[65]

yet only some species' venom cause an adverse reaction in humans.When a nematocyst is triggered by contact by predator or prey, pressurebuilds up rapidly inside it up to 2,000 pounds per square inch(14,000 kPa) until it bursts. A lance inside the nematocyst pierces thevictim's skin, and poison flows through into the victim.[66] Touching orbeing touched by a jellyfish can be very uncomfortable, sometimesrequiring medical assistance; sting effects range from no effect toextreme pain to death. Even beached and dying jellyfish can still stingwhen touched.

Scyphozoan jellyfish stings range from a twinge to tingling to agony.[67] Most jellyfish stings are not deadly,but stings of some species of the class Cubozoa and the Box jellyfish, such as the famous and especially toxicIrukandji jellyfish, can be deadly. Stings may cause anaphylaxis, which can be fatal. Medical care may includeadministration of an antivenom.

In 2010, at a New Hampshire beach, pieces of a single dead lion's mane jellyfish stung between 125 and 150people.[68][69] Jellyfish kill 20 to 40 people a year in the Philippines alone.[67] In 2006 the Spanish Red Crosstreated 19,000 stung swimmers along the Costa Brava.[67]

An Australian box jellyfish called the sea wasp can kill a grown man in a matter of seconds or minutes. Becausethe harpoons are so shallow, however, Australians have learned that they can protect themselves whileswimming in sea wasp waters simply by covering their exposed skin with pantyhose.[2]

Treatment

The three goals of first aid for uncomplicated stings are to prevent injuryto rescuers, deactivate the nematocysts, and remove tentacles attached tothe patient. Rescuers usually wear barrier clothing, such as pantyhose,wet suits or full-body sting-proof suits while removing jellies ortentacles from injured. Deactivating the nematocysts (stinging cells)prevents further injection of venom.

Vinegar (3–10% aqueous acetic acid) may be used as a common remedyto help with box jellyfish stings,[70][71] but not the stings of thePortuguese Man o' War (which is not a true jellyfish, but a colony).[70]

For stings on or around the eyes, a towel dampened with vinegar may beused to dab around the eyes, with care taken to avoid the eyeballs. Saltwater may be used as an alternative if vinegar is unavailable;[70][72] andmay be preferred over vinegar.[73] Fresh water is not usually used if the

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sting occurs in salt water, as changes in tonicity[74] can release additional venom. Rubbing wounds, or usingalcohol, spirits, ammonia, or urine may have strongly negative effects as these can encourage the release ofvenom.[75]

Clearing the area of jelly, tentacles, and wetness further reduces nematocyst firing.[75] Scraping the affectedskin with a knife edge, safety razor, or credit card may remove remaining nematocysts.[76]

Beyond initial first aid, antihistamines such as diphenhydramine (Benadryl) may control skin irritation(pruritus).[76] Ice or fresh water is not usually applied to stings, since they may cause nematocysts to continue torelease toxin.[77][78] Immunobased antivenins have been available since the 1970s;[79] administration requiresmedical personnel and refrigeration and are used in extreme cases as with regard to the box jellyfish,Chironex.[80]

Hazards

Jellyfish adversely affect humanity by interfering with public systems and harming swimmers.[67] The mostobvious consequences are human injury or death and reduced coastal tourism. Jellies destroy fish nets, poison orcrush captured fish, and consume fish eggs and young fish.[81]

Jellyfish can clog cooling equipment, disabling power plants in several countries. Jellyfish caused a cascadingblackout in the Philippines in 1999,[67] as well as damaging the Diablo Canyon Power Plant in California in2008.[82] Clogging can stop desalination plants, as well as clogging ship engines[81] and infesting fishingnets.[83]

References in media

"Jellyfish Invasion" was an episode of the National Geographic Channel documentary seriesExplorer,[84][85][86] which includes research conducted by scientists in Australia, Hawaii and Japan.

The Disney Pixar animated film Finding Nemo illustrated the nearly fatal effects of swimming through ajellyfish bloom. The opening sequence of the animated film Ponyo depicts a massive jellyfish bloom off thecoast of Japan. The Japanese science fiction film Dogora features jellyfish-like space creatures. The Japaneseanime Kuragehime features a main character who is obsessed with jellyfish, and has jellyfish related plotlines.The "A Star is Born Again" episode of The Simpsons depicts a Jellyfish Festival, celebrating the bloom ofjellyfish that overruns the waters and beach.

In the Will Smith movie Seven Pounds, Will Smith's character had a pet jellyfish which played an importantrole at the end of the movie.

On an episode of Survivor Palau, the team winning the reward challenge got to swim in Jellyfish Lake, a lakefull of moon and golden jellyfish, which are harmless to humans.

Taxonomy

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See also: alpha taxonomy, Linnean taxonomy, taxon, and binomial nomenclature

Taxonomic classification systematics within the Cnidaria, as with all organisms, are always in flux. Manyscientists who work on relationships between these groups are reluctant to assign ranks, although there isgeneral agreement on the different groups, regardless of their absolute rank. Presented here is one scheme,which includes all groups that produce medusae (jellyfish), derived from several expert sources:

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Jellyfish taxonomy (phylum Cnidaria: subphylum Medusozoa)Class Subclass Order Suborder Families

Hydrozoa[87][88]

Hydroidolina

AnthomedusaeFilifera see [87]

Capitata see [87]

LeptomedusaeConica see [87]

Proboscoida see [87]

Siphonophorae

PhysonectaeAgalmatidae, Apolemiidae, Erennidae,Forskaliidae, Physophoridae, Pyrostephidae,Rhodaliidae

Calycophorae Abylidae, Clausophyidae, Diphyidae,Hippopodiidae, Prayidae, Sphaeronectidae

Cystonectae Physaliidae, Rhizophysidae

Trachylina

Limnomedusae Olindiidae, Monobrachiidae,Microhydrulidae, Armorhydridae

Trachymedusae Geryoniidae, Halicreatidae, Petasidae,Ptychogastriidae, Rhopalonematidae

Narcomedusae Cuninidae, Solmarisidae, Aeginidae,Tetraplatiidae

Actinulidae Halammohydridae, Otohydridae

Staurozoa[89]Eleutherocarpida Lucernariidae, Kishinouyeidae, Lipkeidae,

Kyopodiidae

Cleistocarpida Depastridae, Thaumatoscyphidae,Craterolophidae

Cubozoa [90] Carybdeidae, Alatinidae, Tamoyidae,Chirodropidae, Chiropsalmidae

Scyphozoa[91][92][93]

Coronatae Atollidae, Atorellidae, Linuchidae,Nausithoidae, Paraphyllinidae, Periphyllidae

Semaeostomeae Cyaneidae, Drymonematidae, Pelagiidae,Phacellophoridae, Ulmaridae

RhizostomeaeCassiopeidae, Catostylidae, Cepheidae,Lobonematidae, Lychnorhizidae, Mastigiidae,Rhizostomatidae, Stomolophidae,Thysanostomatidae, Versurigidae

Haeckel's medusaeIllustrations of medusae by German biologist Ernst Haeckel:

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Narcomedusae

Discomedusae

Trachomedusae

Discomedusae

Leptomedusae

Peromedusae

Anthomedusae

Stauromedusae

Cubomedusae (modernCubozoa)

Discomedusae

Discomedusae

See alsoJellyfish dermatitisList of prehistoric medusozoansOcean sunfish, a significant jellyfish predator

References

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External linksExplore Jellyfish – Smithsonian Ocean Portal (http://ocean.si.edu/ocean-portal-generated-tags/jellyfish)Jellyfish and Other Gelatinous Zooplankton (http://jellieszone.com/)Jellyfish Facts – Information on Jellyfish and Jellyfish Safety (http://www.jellyfishfacts.net/)Cotylorhiza tuberculata (http://www.malawicichlidhomepage.com/other/cotylorhiza_tuberculata.html)"There's no such thing as a jellyfish (https://www.youtube.com/watch?v=3HzFiQFFQYw)" from TheMBARI YouTube channel

Photos:

Jellyfish Exhibition At National Aquarium, Baltimore, Maryland (USA) – Photo Gallery(http://picasaweb.google.com/sridhar.saraf.pictures/JellyfishExhibitionAtNationalAquariumBaltimoreMa

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rylandUSA/)

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