Everything about Jellyfish totally explained
Jellyfish are marine
invertebrates belonging to the
class Scyphozoa of the
phylum Cnidaria. They can be found in every
ocean in the world and even in some fresh water. The term "jellyfish" is a common name, and therefore doesn't imply any systematic relationship to vertebrate fish — jellyfish are
cnidarians. The term "jellyfish" is also applied to some close relatives of true scyphozoans, such as the
Hydrozoa and the
Cubozoa.
Anatomy and morphology
The body of an adult jellyfish consists of a bell shape producing jelly and enclosing its internal structure, from which
tentacles are suspended. Each tentacle is covered with
cells called
cnidocytes, that can sting or kill other animals. Most jellyfish use these cells to secure prey or for defense. Others, such as the
Rhizostomae, don't have tentacles at all.
Jellyfish lack basic sensory organs and a
brain, but their
nervous systems and
rhopalia allow them to perceive stimuli, such as light and odor, and respond quickly. They feed on small
fish and
zooplankton that become caught in their tentacles. Most jellyfish are passive drifters and slow swimmers, as their shape isn't
hydrodynamic. Instead, they move so as to create a current forcing the prey within reach of their tentacles. They do this by rhythmically opening and closing their bell-like body. Their
digestive system is incomplete: the same orifice is used to take in food and expel waste.
The body of an adult is made up of 94–98% water. The bell consists of a layer of
epidermis,
gastrodermis, and a thick, intervening layer called
mesoglea that produces most of the jelly.
Body systems
A jellyfish detects the touch of other animals using a nervous system called a "
nerve net", located in its
epidermis. Touch stimuli are conducted by nerve rings, through the
rhopalial lappet, located around the animal's body, to the nerve cells. Jellyfish also have
ocelli: light-sensitive organs that don't form images but are used to determine up from down, responding to sunlight shining on the water's surface.
Jellyfish don't have a specialized
digestive,
osmoregulatory,
central nervous,
respiratory, or
circulatory systems. They digest using the
gastrodermal lining of the
gastrovascular cavity, where nutrients are absorbed. They don't need a respiratory system since their skin is thin enough that the body is oxygenated by
diffusion. They have limited control over movement and mostly free-float, but can use the
hydrostatic skeleton of the water pouch to accomplish vertical movement through pulsations of the disc-like body.
The outer side of a jellyfish is lined with a jelly-like material called
ectoplasm (
ecto meaning outer and
plasm meaning living matter). The ectoplasm typically contains a smaller amount of
protein granules and other
organic compounds than inner cytoplasm, also referred to as
endoplasm (
endo meaning inner).
Jellyfish blooms
Many species of jellyfish are capable of congregating into large
swarms or "blooms", consisting of hundreds of individuals. The formation of these blooms is a complex process that depends on
ocean currents,
nutrients, temperature and ambient oxygen concentrations. Jellyfish sometimes mass breed during blooms. During such times of rapid population expansion, some people will raise
ecological concerns about the potential noxious effects of a jellyfish "outbreak".
According to Claudia Mills of the
University of Washington, the frequency of jellyfish blooms may be attributed to man's impact on marine systems. She says that the breeding jellyfish may merely be filling
ecological niches formerly occupied by
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 nutrients in the water, ascribed to agricultural
runoff, have also been cited as an antecedent to the proliferation of jellyfish. Monty Graham, of the
Dauphin Island Sea Lab in
Alabama, says that "ecosystems in which there are high levels of nutrients ... provide nourishment for the small organisms on which jellyfish feed. In waters where there's
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."
By sampling sea life in a heavily fished region off the coast of
Namibia, researchers found that jellyfish have overtaken fish in terms of
biomass. The findings represent a careful, quantitative analysis of what has been called a "jellyfish explosion" following intense fishing in the area in the last few decades. The findings were reported by Andrew Brierley of the University of St. Andrews and his colleagues in the July 12, 2006 issue of the journal
Current Biology.
Areas which have been seriously affected by jellyfish blooms include the northern
Gulf of Mexico. In that case, Graham states, "Moon jellies have formed a kind of gelatinous net that stretches from end to end across the gulf."
Importance to humans
Culinary uses
Jellyfish are an important source of food to the Chinese community and in many Asian countries. Only jellyfish belonging to the
order Rhizostomeae are harvested for food. Rhizostomes, especially
Rhopilema esculentum in China (Chinese name:
hǎizhē) and
Stomolophus meleagris (cannonball jellyfish) in the United States, are favoured because they're typically larger and have more rigid bodies than other scyphozoans. Furthermore, their toxins are innocuous to humans. Desalted, ready-to-eat products are also available. Jellyfish are also harvested for their
collagen, which can be used for a variety of scientific applications including the treatment of
rheumatoid arthritis.
In captivity
Jellyfish are commonly displayed in aquaria in many countries. Often the tank's background is blue and the animals are illuminated by side light to produce a high contrast effect. In natural conditions, many jellies are so transparent that they're almost impossible to see.
Holding jellyfish in captivity presents other problems. For one, they're not adapted to closed spaces. They depend on currents to transport them from place to place. To compensate for this, professional exhibits feature precise water flows, typically in circular tanks to prevent specimens from becoming trapped in corners. The Monterey Bay Aquarium uses a modified version of the
kreisel (German for "spinning top") for this purpose.
Toxicity to humans
When stung by a jellyfish,
first aid may be needed immediately. The stings of true Scyphozoan jellyfish are not generally deadly, though species of the completely separate class
Cubozoa (box jellyfish) such as the famous and especially toxic
Irukandji can be fatal. However, even nonfatal jellyfish stings are known to be extremely painful. Serious stings may cause anaphylaxis and may result in death. Hence, people stung by jellyfish must get out of the water to avoid drowning. In 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 into the patient.
Vinegar (3 to 10% aqueous
acetic acid) should be applied for
box jellyfish stings. Vinegar, however, isn't recommended for
Portuguese Man o' War stings. Fresh water shouldn't be used if the sting occurred in salt water, as a change in
pH can cause the release of additional venom. Rubbing the wound, or using
alcohol, spirits,
ammonia, or
urine will encourage the release of venom and should be avoided. Though often not available, a shower or bath as hot as can be tolerated can neutralize stings. However, if
hypothermia is suspected this method may cause other serious complications.
Once deactivated, the stinging cells must be removed. This can be accomplished by picking off tentacles left on the body.
Beyond initial first aid,
antihistamines such as
diphenhydramine (
Benadryl) may be used to control skin irritation (
pruritus).
To remove the venom in the skin, apply a paste of baking soda and water and apply a cloth covering on the sting. If possible, reapply paste every 15-20 minutes. Ice can be applied to stop the spread of venom until either of these is available.
Further Information
Get more info on 'Jellyfish'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://jellyfish.totallyexplained.com">Jellyfish Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
