Jellyfish are found in every ocean, from the surface to the deep sea. A few
jellyfish inhabit freshwater. Large, often colorful, jellyfish are common in
coastal zones worldwide. Jellyfish have roamed the seas for at least 500 million
years, and possibly 700 million years or more, making them the oldest
multi-organ animal.
Terminology
The term medusa was coined by Linnaeus in 1752, alluding to the
tentacled head of Medusa in Greek mythology. This term refers exclusively to
the non-polyp life-stage which occurs in many cnidarians, which is typified by
a large pulsating gelatinous bell with long trailing tentacles. All
medusa-producing species belong to the sub-phylum medusozoa.
The English popular name jellyfish has been in use since 1796. It
has traditionally also been applied to other animals sharing a superficial
resemblance, for example ctenophores (members from another phylum of common,
gelatinous and generally transparent or translucent, free-swimming planktonic
carnivores now known as comb jellies) were included as
"jellyfishes". Even some scientists include the phylum ctenophora
when they are referring to jellyfish. Other scientists prefer to use the more
all-encompassing term gelatinous zooplankton, when referring to these, together
with other soft-bodied animals in the water column.
As jellyfish are not even vertebrates, let alone true fish, the usual word jellyfish
is considered by some to be a misnomer, and American public aquariums have
popularized use of the terms jellies or sea jellies instead.
Many textbooks and websites refer to only scyphozoans as "true
jellyfish".
A group of jellyfish is sometimes called a bloom or a swarm.
"Bloom" is usually used for a large group of jellyfish that gather in
a small area, but may also have a time component, referring to seasonal
increases, or numbers beyond what was expected. Another collective name for a
group of jellyfish is a smack, although this term is not
commonly used by scientists who study jellyfish. Jellyfish are
"bloomy" by nature of their life cycles, being produced by their
benthic polyps usually in the spring when sunshine and plankton increase, so
they appear rather suddenly and often in large numbers, even when an ecosystem
is in balance. Using "swarm" usually implies some kind of active
ability to stay together, which a few species such as Aurelia, the moon
jelly, demonstrate.
Medusa jellyfish may be classified as scyphomedusae ("true"
jellyfish), stauromedusae (stalked jellyfish), cubomedusae (box jellyfish), or
hydromedusae, according to which clade their species belongs to.
In biology, a medusa (plural: medusae) is a form of cnidarian in
which the body is shaped like an umbrella, in contrast with polyps. Medusae
vary from bell-shaped to the shape of a thin disk, scarcely convex above and
only slightly concave below. The upper or aboral surface is called the exumbrella
and the lower surface is called the subumbrella; the mouth is located on
the lower surface, which may be partially closed by a membrane extending inward
from the margin (called the velum). The digestive cavity consists of the
gastrovascular cavity and radiating canals which extend toward the margin;
these canals may be simple or branching, and vary in number from few to many.
The margin of the disk bears sensory organs and tentacles as its said.
German biologist Ernst Haeckel popularized medusae through his vivid
illustrations, particularly in Kunstformen der Natur.
Anatomy
Most jellyfish do not have specialized digestive, osmoregulatory, central
nervous, respiratory, or circulatory systems. The manubrium is a stalk-like
structure hanging down from the centre of the underside, with the mouth at its
tip. This opens into the gastrovascular cavity, where digestion takes place and
nutrients are absorbed. It is joined to the radial canals which extend to the
margin of the bell. Jellyfish do not need a respiratory system
since their skin is thin enough that the body is oxygenated by diffusion. They
have limited control over movement, but can use their hydrostatic skeleton to
navigate through contraction-pulsations of the bell-like body; some species
actively swim most of the time, while others are mostly passive. The Jellyfish body consist
of over 95% water; most of their umbrella mass is a gelatinous material—the
jelly—called mesoglea which is surrounded by two layers 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 have no brain nor central nervous system, but employ a loose
network of nerves, located in the epidermis, which is called a "nerve
net". A jellyfish detects various stimuli including
the touch of other animals via this nerve net, which then transmits impulses
both throughout the nerve net and around a circular 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 to
control their location. In Roscoe Bay, jellyfish ride the current at ebb tide
until they hit a gravel bar, and then descend below the current. They remain in
still waters waiting for the tide to rise, ascending and allowing it to sweep
them back into the bay. They monitor salinity to avoid fresh water from
mountain snowmelt, again by diving until they find enough salt.
Vision
Some jellyfish also have ocelli: light-sensitive organs that do not form images
but which can detect light, and are used to determine up from down, responding
to sunlight shining on the water's surface. These are generally pigment 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 their counterparts. The Box jellyfish has 24 eyes, two
of which are capable of seeing color, and four parallel information processing
areas or rhopalia that act in competition, supposedly making it one of the only
creatures to have a 360 degree view of its environment. It is suggested
that the two eyes that contain cornea and retina are attached to a central
nervous system which enables the four brains to process images. It is unknown
how this works, as the creature has a unique central nervous system.
The eyes are suspended on stalks with heavy crystals on one end, acting
like a gyroscope to orient the eyes skyward. They look upward to navigate from
roots in mangrove swamps to the open lagoon and back, watching for the mangrove
canopy, where they feed.
Size
The lion's mane jellyfish Cyanea capillata is one of the larger
species of jellyfish.
Jellyfish range from about one millimeter in bell height and diameter to nearly two meters in bell height and diameter; 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 have bell disks from 0.5 mm to a few mm
diameter, with short tentacles that extend out beyond this, on which these tiny
jellyfish crawl around on seaweed or the bottoms of rocky pools. Many of these
tiny creeping jellyfish cannot 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 many species that have just been released from their parent polyps; some of
these live only a few minutes before shedding their gametes in the plankton and
then dying, while others will grow in the plankton for weeks or months. The
hydromedusae Cladonema radiatum and Cladonema californicum are
also very small, living for months, yet never growing beyond a few mm in bell
height and diameter. Another small species of jellyfish is the
Australian Irukandji, which is about the size of a fingernail.
The lion's mane jellyfish, Cyanea capillata, was long-cited as the
largest jellyfish, and arguably the longest animal in the world, with fine, thread-like
tentacles that may extend up to 36.5 metres (120 ft) long (though most are
nowhere near that large). They have a moderately painful, but rarely
fatal, sting. Claims that this jellyfish may be the longest animal in the world
are likely exaggerated; some other planktonic cnidarians called siphonophores
may typically be tens of meters long and seem a more legitimate candidate for
longest animal.
The increasingly common giant Nomura's jellyfish, Nemopilema nomurai,
found in some, but not all years in the waters of Japan, Korea and China in
summer and autumn is probably a much better candidate for "largest
jellyfish", since the largest Nomura's jellyfish in late autumn can reach
200 centimetres (79 in) in bell (body) diameter and about 200 kilograms (440 lb)
in weight, with average specimens frequently reaching 90 centimetres
(35 in) in bell diameter and about 150 kilograms (330 lb) in weight.
The large bell mass of the giant Nomura's jellyfish can dwarf a
diver and is nearly always much greater than the up-to-100 centimetres
(39 in) bell diameter Lion's Mane.
The rarely-encountered deep-sea jellyfish Stygiomedusa gigantea is
another solid candidate for "largest jellyfish", with its thick,
massive bell up to 100 centimetres (39 in) wide, and four thick,
"strap-like" oral arms extending up to 6 metres (20 ft) in
length, very different from the
typical fine, threadlike tentacles that rim the umbrella of
more-typical-looking jellyfish, including the Lion's Mane.
Classification and evolution
Medusa jellyfish are a life stage exhibited in some species of the phylum
cnidaria. Medusa jellyfish belong exclusively to medusozoa, the clade of
cnidarians which excludes anthozoa (e.g., corals and anemones). (This suggests
that the medusa form evolved after the polyps.)
The phylogenetics of this group are complex and still being worked out.
Some progress has been made: the Medusozoa appear to be a sister group to
Octocorallia. Staurozoa appears to be the earliest
diverging; Cubozoa and the coronate Scyphozoa form a clade that is the sister
group of Hydrozoa plus discomedusan Scyphozoa. The Hydrozoa are the sister
group of discomedusan Scyphozoa. Limnomedusae (Trachylina) is the sister group
of hydroidolinans. This group may be the earliest diverging lineage among Hydrozoa.
Semaeostomeae is a paraphyletic clade with Rhizostomeae.
There are four major classes of medusozoan cnidaria:
- Scyphozoa are often called true jellyfish. They have tetra-radial symmetry. They have tentacles around the 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.
- Hydrozoa may form medusa which resemble scyphozoans (but generally with a velum) and are distinguished by an absence of cells in the mesoglea. However, many hydrozoa species do not form medusa at all (such as hydra, which is hence not considered a jellyfish).
- Staurozoa (stalked jellyfish) do not have a polyp stage, however the medusa is generally sessile, oriented upside down and with a stalk from the "bell" planted to the substrate. Until recently, staurozoa was classified within scyphozoa.
Some other animals are frequently associated with or mistaken for medusa
jellyfish.
- Siphonophorae are an order of hydrozoa which generally live as colonies (for example, free swimming chains of repeated units, some units similar to polyps or to medusa). They are not considered medusa jellyfish. A well known example is the Portuguese Man o' War.
- Ctenophores (comb jellies) are a separate phylum from cnideria. Their method of propolsion is cillia paddles rather than a pulsating bell.
- Salps are transparent, gelatinous marine organisms that form pelagic colonies like siphonophores. Salps are chordates, and as such are actually more closely related to humans than they are to cnidarians and comb jellies.
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 species that do not).
Life-cycle
Most jellyfish alternate between polyp and medusa generations
during their 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 small larva covered with cilia. It settles onto a
firm surface and develops into a polyp. Some polyps can also asexually produce
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 polyps are like miniatures of the closely related
anthozoan (sea anemones and corals) polyps, which are also members of Cnidaria.
The jellyfish polyp may be sessile, living on the bottom or another substrate
such as floats or boat hulls, or it may be free-floating or attached to tiny
bits of free-living plankton or rarely, fish or other invertebrates. Polyps may
be solitary or colonial. Polyp colonies form by strobilation, resulting in
multiple polyps which share a common stomach cavity. Most polyps are
very small, measured in millimeters. They 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 strobilation or 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 is enough food. In most species, spawning is
controlled by light, so the entire population spawns at about the same time of
day, often at either dusk or dawn. Jellyfish are usually either male or female
(hermaphroditic specimens are occasionally found).
In most cases, adults release sperm and eggs into the surrounding water,
where the (unprotected) eggs are fertilized and mature into new organisms. In a
few species, the sperm swim into the female's mouth fertilizing the eggs within
the female's body where they remain during early development stages. In moon
jellies, the eggs lodge in pits on the oral arms, which form a temporary brood
chamber for the developing planula larvae.
After a growth interval, the polyp begins reproducing asexually by budding
and, in the Scyphozoa, is called a segmenting polyp, or a scyphistoma.
New scyphistomae may be produced by budding or form new, immature jellies
called ephyrae. A few jellyfish species can produce 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 of hydromedusae reproduce by fission
(splitting in half).
In the second stage, the tiny polyps asexually produce jellyfish, each of
which is also known as a medusa. Tiny jellyfish (usually only a
millimeter or two across) swim away from the polyp and then grow and feed in
the plankton . Medusae have a radially symmetric, umbrella-shaped body
called a bell, which is usually supplied with marginal tentacles -
fringe-like protrusions from the bell's border that capture prey. A few species
of jellyfish do not have the polyp portion of the life cycle, but go from
jellyfish to the next generation of jellyfish through direct development of
fertilized eggs.
Most jellyfish have a second stage to their life cycle, the planula larvae
phase, following the initial egg and sperm phase. Although this is a short
lived stage for jellyfish, it is an important phase when the fertilized eggs
that had previously undergone embryonic development, hatch, and planulae emerge
from the females mouth or brood pouch and are off on their own.
Lifespan
Jellyfish lifespans typically range from a few hours (in the case of some
very small hydromedusae) to several months. 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 they develop infections, so may live several years, though this
would be very unusual in the sea. Most large coastal jellyfish 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. Another
unusual species, T. nutricula, falsely reported as Turritopsis
dohrnii, might be effectively immortal because of its ability under certain
circumstances in the laboratory to transform from medusa back to the polyp
stage, thereby escaping the death that typically awaits medusae
post-reproduction if they have not otherwise been eaten by some other ocean
organism . So far this transdifferentian of life form has been observed only in
the laboratory and it is not known 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 and voiding 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 which specialize in jellies. Other predators
include tuna, shark, swordfish, sea turtles and at least one species of Pacific
salmon. 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
Aurelia sp. occurs in large quantities in most of the world's coastal waters. Members
of this genus are nearly identical to each other.
Map of population trends of native and invasive species of jellyfish
Increase (high certainty)
Increase (low certainty)
Stable/variable
Decrease
No data
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 to congregate
jellyfish into large swarms or "blooms", consisting of hundreds or
thousands of individuals. Blooms can 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 may also benefit from saltier waters,
as saltier waters contain more iodine, which is necessary for polyps to turn
into jellyfish. Rising sea temperatures caused by climate change may also
contribute to jellyfish blooms, because many species of jellyfish are
relatively better able to survive in warmer waters.
Scientists have little historic data about jellyfish populations.
One hypothesis is that the global increase in jellyfish bloom frequency may
stem from human impact. In some locations jellyfish may be filling ecological
niches formerly occupied by now overfished creatures, but this hypothesis lacks
supporting data. Youngbluth states that "jellyfish feed on
the same kinds of prey as adult and young fish, so if fish are removed from the
equation, jellyfish are likely to move in."
Some jellyfish populations that have shown clear increases in the past few
decades are invasive species, newly arrived from other habitats: examples
include the Black Sea, Caspian Sea, Baltic Sea, central and eastern
Mediterranean, Hawaii, and tropical and subtropical parts of the West Atlantic
(including the Caribbean, Gulf of Mexico and Brazil). Invasive populations
can expand rapidly because they often face no predators in the new habitat.
Increased nutrients, ascribed to agricultural runoff, have been cited as
contributing to jellyfish proliferation. Graham states, "ecosystems in
which there are high levels of nutrients ... 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."
Population
Jellyfish populations may be expanding globally as a result of overfishing
and the availability of excessive nutrients due to land runoff.
When marine ecosystems become disturbed
jellyfish can proliferate. For example, jellyfish reproduce rapidly and have
fast growth rates; they predate many species, while few species predate them;
and they feed via touch rather than visually, so they can feed effectively at
night and in turbid waters. It may become difficult for fish stocks to
reestablish themselves in marine ecosystems once they have become dominated by
jellyfish, because jellyfish feed on plankton, which includes fish eggs and
larvae.
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 in the plankton, a few species of jellyfish
are closely associated with the bottom for much of their lives (that is, they
can be considered benthic). The upside-down jellyfish in the genus Cassiopea
typically lie on the bottom of shallow lagoons where they sometimes pulsate
gently with their umbrella top facing down. The tiny creeping jellyfish Staurocladia
and Eleutheria (see section on Size, above) cannot swim and
"walk" around on seaweed fronds or rocky bottoms on their tentacles.
Most hydromedusae and scyphomedusae that live in coastal habitats find
themselves on the bottom periodically, where they may stop swimming for awhile,
and certain box jellyfish species also rest on the sea bed in shallow water. Even some deep-sea species
of hydromedusae and scyphomedusae are usually collected on or near the bottom.
All of the stauromedusae are found attached to either seaweed or rocky or other
firm material on the bottom.
Relationship to humans
Culinary
Cannonball jellyfish, Stomolophus meleagris, are harvested for
culinary purposes.
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 spoil
within a matter of hours. Once dried, they can be stored for weeks at a time.
Only scyphozoan jellyfish belonging to the order Rhizostomeae are harvested for
food; about 12 of the approximately 85 species. Most of the harvest takes place
in southeast Asia. Rhizostomes, especially Rhopilema esculentum in
China (海蜇 hǎizhē, "sea stings") and Stomolophus meleagris
(cannonball jellyfish) in the United States, are favored because of their
larger and more rigid bodies and because their toxins are harmless to humans.
Rehydrated jellyfish strips prepared with soy sauce, sesame oil, and chili
sauce
Traditional processing methods, carried out by a Jellyfish Master,
involve a 20 to 40 day multi-phase procedure in which after removing the gonads
and mucous membranes, the umbrella and oral arms are treated with a mixture of
table salt and alum, and compressed. Processing reduces liquefaction, odor, the
growth of spoilage organisms, and makes the jellyfish drier and more acidic,
producing a "crunchy and crispy texture." Jellyfish prepared this way
retain 7-10% of their original weight, and the processed product contains
approximately 94% water and 6% protein. Freshly processed jellyfish has a
white, creamy color and turns yellow or brown during prolonged storage.
In China, processed jellyfish are desalted by soaking in water overnight
and eaten cooked or raw. The dish is often served shredded with a dressing of
oil, soy sauce, vinegar and sugar, or as a salad with vegetables. In Japan,
cured jellyfish are rinsed, cut into strips and served with vinegar as an
appetizer. Desalted, ready-to-eat products are also
available.
Fisheries
Global harvest of jellyfish in thousands of tonnes as reported by the FAO
Fisheries have begun harvesting the American cannonball jellyfish, Stomolophus
meleagris, along the southern Atlantic coast of the United States and in
the Gulf of Mexico for export to Asia.
Jellyfish are also harvested for their collagen, which can be used for a
variety of applications including the treatment of rheumatoid arthritis.
Biotechnology
The hydromedusa Aequorea victoria
In 1961, Osamu Shimomura extracted green fluorescent protein (GFP) and
another bioluminescent protein, called aequorin, from the large and abundant
hydromedusa Aequorea victoria, while studying photoproteins that cause
bioluminescence in this species. Three decades later, Douglas Prasher sequenced
and cloned the gene for GFP. Martin Chalfie figured out how to use GFP as a
fluorescent marker of genes inserted into other cells or organisms. Roger Tsien
later chemically manipulated GFP to produce other fluorescent colors to use as
markers. In 2008, Shimomura, Chalfie and Tsien won the Nobel Prize in Chemistry
for their work with GFP.
Man-made GFP became commonly used as a fluorescent tag to show which cells
or tissues express specific genes. The genetic engineering technique fuses the
gene of interest to the GFP gene. The fused DNA is then 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 artificial gene turns on in the same
tissues and the same time as the normal gene, making GFP instead of the normal
protein. Illuminating the animal or cell reveals what tissues express that
protein—or at what stage of development. The fluorescence shows where the gene
is expressed.
Aquaria
A group of Pacific sea nettle jellyfish, Chrysaora fuscescens, in an
aquarium exhibit
Jellyfish are displayed in many public aquaria. Often the tank's background
is blue and the animals are illuminated 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 in corners. The
Monterey Bay Aquarium uses a modified version of the kreisel (German for
"spinning top") for this purpose. As of 2009, jellyfish were becoming
popular in home aquaria.
Toxicity
Jellyfish sting their prey using nematocysts, also called cnidocysts,
stinging structures located in specialized cells called cnidocytes, which are
characteristic of all Cnidaria. Contact with a jellyfish tentacle can trigger
millions of nematocysts to pierce the skin and inject venom, yet only some
species' venom cause an adverse reaction in humans. When a nematocyst is
triggered by contact by predator or prey, pressure builds up rapidly inside it
up to 2,000 pounds per square inch (14,000 kPa) until it bursts. A lance
inside the nematocyst pierces the victim's skin, and poison flows through into
the victim. Touching or being touched by a jellyfish can
be very uncomfortable, sometimes requiring medical assistance; sting effects
range from no effect to extreme pain to death. Even beached and dying jellyfish
can still sting when touched.
Scyphozoan jellyfish stings range from a twinge to tingling to agony.
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 toxic Irukandji jellyfish, can be deadly. Stings
may cause anaphylaxis, which can be fatal. Medical care may include
administration of an antivenom.
In 2010, at a New Hampshire beach, pieces of a single dead lion's mane
jellyfish stung between 125 and 150 people. Jellyfish kill 20 to 40 people a year in the
Philippines alone. In 2006 the Spanish Red Cross treated 19,000
stung swimmers along the Costa Brava.
An Australian box jellyfish called the sea wasp can kill a grown man in a
matter of seconds or minutes. Because the harpoons are so shallow, however,
Australians have learned that they can protect themselves while swimming in sea
wasp waters simply by covering their exposed skin with pantyhose.
Treatment
The three goals of first aid for uncomplicated stings are to prevent injury
to rescuers, deactivate the nematocysts, and remove tentacles attached to the
patient. Rescuers need to wear barrier clothing, such as pantyhose, wet suits
or full-body sting-proof suits. Deactivating the nematocysts (stinging cells)
prevents further injection of venom.
Like many species of jellyfish, the sting of some species of Mastigias
have little or no discernible effect on humans.
Vinegar (3–10% aqueous acetic acid) is a common remedy to help with box
jellyfish stings, but not the stings of the Portuguese Man o' War (which is not
a true jellyfish, but a colony). For stings on or around the eyes, a towel
dampened with vinegar is used to dab around the eyes, with care taken to avoid
the eyeballs. Salt water is an alternative if vinegar is unavailable.
Fresh water is not used if the sting occurs in
salt water, as changes in tonicity can release additional venom. Rubbing
wounds, or using alcohol, spirits, ammonia, or urine may have strongly negative
effects as these can encourage the release of venom.
Clearing the area of jelly, tentacles, and wetness further reduces
nematocyst firing. Scraping the affected skin with a knife edge,
safety razor, or credit card can remove remaining nematocysts.
Beyond initial first aid, antihistamines such as diphenhydramine (Benadryl)
can control skin irritation (pruritus). For removal of venom in the skin, a paste of
baking soda and water can be applied with a cloth covering on the sting. In some
cases it is necessary to reapply paste every 15–20 minutes. Ice or fresh water
should not be applied to the sting, as this may help the nematocysts to
continue to release toxin.
Hazards
Jellyfish adversely affect humanity by interfering with public systems and
harming swimmers. The most obvious consequences are human injury
or death and reduced coastal tourism. Jellies destroy fish nets, poison or
crush captured fish, and consume fish eggs and young fish.
Jellyfish can clog cooling equipment, disabling power plants in several
countries. Jellyfish caused a cascading blackout in the Philippines in 1999, as well as
damaging the Diablo Canyon Power Plant in California in 2008. Clogging can
stop desalination plants, as well as clogging ship engines and infesting
fishing nets.
Media presence
"Jellyfish Invasion" was an episode of the National Geographic
Channel documentary series Explorer, 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 a jellyfish bloom. The opening sequence of
the animated film Ponyo depicts a massive jellyfish bloom off the coast
of Japan. The Japanese science fiction film Dogora features
jellyfish-like space creatures. The Japanese anime 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 of jellyfish that overruns
the waters and beach.
In the Will Smith movie Seven Pounds, Will Smith's character had a
pet jellyfish which played an important role 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 lake full of moon and golden jellyfish, which
are harmless to humans.
Taxonomy
Taxonomic classification systematics within the Cnidaria, as with all
organisms, are always in flux. Many scientists who work on relationships
between these groups are reluctant to assign ranks, although there is general
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:
Jellyfish taxonomy (phylum Cnidaria: subphylum Medusozoa)
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Class
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Subclass
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Order
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Suborder
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Families
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Hydrozoa
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Hydroidolina
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Anthomedusae
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Filifera
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Capitata
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Leptomedusae
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Conica
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Proboscoida
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Siphonophorae
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Physonectae
|
Agalmatidae, Apolemiidae, Erennidae, Forskaliidae, Physophoridae,
Pyrostephidae, Rhodaliidae
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Calycophorae
|
Abylidae, Clausophyidae, Diphyidae, Hippopodiidae, Prayidae,
Sphaeronectidae
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Cystonectae
|
Physaliidae, Rhizophysidae
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Trachylina
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Limnomedusae
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Olindiidae, Monobrachiidae, Microhydrulidae, Armorhydridae
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Trachymedusae
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Geryoniidae, Halicreatidae, Petasidae, Ptychogastriidae, Rhopalonematidae
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Narcomedusae
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Cuninidae, Solmarisidae, Aeginidae, Tetraplatiidae
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Actinulidae
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Halammohydridae, Otohydridae
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Staurozoa
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Eleutherocarpida
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Lucernariidae, Kishinouyeidae, Lipkeidae, Kyopodiidae
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Cleistocarpida
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Depastridae, Thaumatoscyphidae, Craterolophidae
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Cubozoa
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Carybdeidae, Alatinidae, Tamoyidae, Chirodropidae, Chiropsalmidae
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Scyphozoa
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Coronatae
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Atollidae, Atorellidae, Linuchidae, Nausithoidae, Paraphyllinidae,
Periphyllidae
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Semaeostomeae
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Cyaneidae, Drymonematidae, Pelagiidae, Phacellophoridae, Ulmaridae
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Rhizostomeae
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Cassiopeidae, Catostylidae, Cepheidae, Lobonematidae, Lychnorhizidae,
Mastigiidae, Rhizostomatidae, Stomolophidae, Thysanostomatidae, Versurigidae
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source :
http://en.wikipedia.org/wiki/Jellyfish
http://bioweb.uwlax.edu
Jelly Fish
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