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Box jellyfish (class Cubozoa) are cnidarian invertebrates distinguished by their cube-shaped medusae. Some species of box jellyfish produce extremely potent venom: Chironex fleckeri, Carukia barnesi and Malo kingi are among the most venomous creatures in the world. Stings from these and a few other species in the class are extremely painful and sometimes fatal to humans.
"Box jellyfish" and "sea wasp" are common names for the highly venomous Chironex fleckeri. However, these terms are ambiguous, as "sea wasp" and "marine stinger" are sometimes used to refer to other box jellyfish.
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Box jellyfish most visibly differ from the Scyphozoan jellyfish in that they are umbrella shaped, rather than domed or crown-shaped. The underside of the umbrella includes a flap, or velarium, concentrating and increasing the flow of water expelled from the umbrella. As a result, box jellyfish can move more rapidly than other jellyfish. In fact, speeds of up to six meters per minute have been recorded.
The box jellyfish's nervous system is also more developed than that of many other jellyfish. Notably, they possess a nerve ring around the base of the umbrella that coordinates their pulsing movements; a feature found elsewhere only in the crown jellyfish. Whereas some other jellyfish do have simple pigment-cup ocelli, box jellyfish are unique in the possession of true eyes, complete with retinas, corneas and lenses. Their eyes are located on each of the four sides of their bell in clusters called rhopalia. This enables them to see specific points of light, as opposed to simply distinguishing between light and the dark. Box jellyfish also have 20 ocelli (simple eyes), that do not form images but detect light and dark; they therefore have a total of 24 eyes. A box jellyfish has the closest thing a known jellyfish has to a brain. Box jellyfish also display complex, probably visually guided behaviors such as obstacle avoidance and fast directional swimming. Tests have shown that they have a limited memory, and have a limited ability to learn. Research indicates that, owing to the number of rhopalial nerve cells and their overall arrangement, visual processing and integration at least partly happen within the rhopalia of box jelly fish.
Some species have tentacles that can reach up to 3 metres in length. Box jellyfish can weigh up to 2 kg.
Although the venomous species of box jellyfish are almost entirely restricted to the tropical Indo-Pacific, various species of box jellyfish can be found widely in tropical and subtropical oceans, including the Atlantic and east Pacific, with species as far north as California, the Mediterranean (e.g., Carybdea marsupialis) and Japan (e.g., Chironex yamaguchii), and as far south as South Africa (e.g., Carybdea branchi) and New Zealand (e.g., Carybdea sivickisi).
The box jellyfish actively hunts its prey (zooplankton and small fish), rather than drifting as do true jellyfish. They are capable of achieving speeds of up to 1.5 to 2 metres per second or about 4 knots (7.4 km/h; 4.6 mph).
A fully grown box jellyfish has a respectable size: it measures up to 20cm along each box side (or 30 cm in diameter), and the tentacles can grow up to 3 metres in length. Its weight can reach 2 kg. There are about 15 tentacles on each corner. Each tentacle has about 500,000 cnidocytes, containing nematocysts, a harpoon-shaped microscopic mechanism that injects venom into the victim. Many different kinds of nematocysts are found in cubozoans.
The venom of cubozoans is distinct from that of scyphozoans, and is used to catch prey (small fish and invertebrates, including prawns and bait fish) and for defence from predators, which include the butterfish, batfish, rabbitfish, crabs (Blue Swimmer Crab) and various species of sea turtles (hawksbill turtle, flatback turtle). Sea turtles, however, are apparently unaffected by the sting and eat box jellyfish.
Box jellyfish can see. They have clusters of eyes on each side of the box. Some of those eyes are surprisingly sophisticated, with a lens and cornea, an iris that can contract in bright light, and a retina. Their speed and vision leads some researchers to believe that box jellyfish actively hunt their prey, others insist they are passive opportunists, meaning they just hang around and wait for prey to bump into their tentacles. They certainly are very good at avoiding even tiny objects and likely attempt to avoid humans..
Although the box jellyfish has been called "the world's most venomous creature", only a few species in the class have been confirmed to be involved in human deaths, and some species pose no serious threat at all. For example, the sting of Chiropsella bart only results in short-lived itching and mild pain.
In Australia, fatalities are most often perpetrated by the largest species of this class of jellyfish Chironex fleckeri. In December 2012, Angel Yanagihara of the University of Hawaii's Department of Tropical Medicine found the venom causes cells to become porous enough to allow potassium leakage, causing hyperkalemia which can lead to cardiovascular collapse and death as quickly as within 2 to 5 minutes. She postulated that a zinc compound may be developed as an antidote.
The recently discovered and very similar Chironex yamaguchii may be equally dangerous, as it has been implicated in several deaths in Japan. It is unclear which of these species is the one usually involved in fatalities in the Malay Archipelago. In 1990, a 4-year-old child died after being stung by Chiropsalmus quadrumanus at Galveston Island in the Gulf of Mexico, and either this species or Chiropsoides buitendijki are considered the likely perpetrators of two deaths in West Malaysia. At least two deaths in Australia have been attributed to the thumbnail-sized Irukandji jellyfish. Those who fall victim to these may suffer severe physical and psychological symptoms, known as Irukandji syndrome. Nevertheless, most victims do survive, and out of 62 people treated for Irukandji envenomation in Australia in 1996, almost half could be discharged home with few or no symptoms after 6 hours, and only two remained hospitalized approximately a day after they were stung.
In Australia, C. fleckeri has caused at least 64 deaths since the first report in 1883, but even in this species most encounters appear to only result in mild envenoming. Most recent deaths in Australia have been in children, which is linked to their smaller body mass. In parts of the Malay Archipelago, the number of lethal cases is far higher (in the Philippines alone, an estimated 20-40 die annually from Chirodropid stings), likely due to limited access to medical facilities and antivenom, and the fact that many Australian beaches are enclosed in nets and have vinegar placed in prominent positions allowing for rapid first aid. Vinegar is also used as treatment by locals in the Philippines.
Box jellyfish are known as the "suckerpunch" of the sea not only because their sting is rarely detected until the venom is injected, but also because they are almost transparent.
In northern Australia, the highest risk period for the box jellyfish is between October and May, but stings and specimens have been reported all months of the year. Similarly, the highest risk conditions are those with calm water and a light, onshore breeze; however, stings and specimens have been reported in all conditions.
In Hawaii, box jellyfish numbers peak approximately 7 to 10 days after a full moon, when they come near the shore to spawn. Sometimes the influx is so severe that lifeguards have closed infested beaches, such as Hanauma Bay, until the numbers subside.
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Once a tentacle of the box jellyfish adheres to skin, it pumps nematocysts with venom into the skin, causing the sting and agonizing pain. Domestic vinegars have been confirmed as an effective treatment as they disable the sea wasp's nematocysts not yet discharged into the bloodstream. Pressure immobilisation can also be used on limbs to slow down the spreading of the deadly venom. Common practice is to apply generous amounts of vinegar prior to and after the stinging tentacle is removed. Removal of additional tentacles is usually done with a towel or gloved hand, to prevent secondary stinging. Tentacles will still sting if separated from the bell, or after the creature is dead. Removal of tentacles without prior application of vinegar may cause unfired nematocysts to come into contact with the skin and fire, resulting in a greater degree of envenomation.
Although commonly recommended in folklore and even some papers on sting treatment, there is no scientific evidence that urine, ammonia, meat tenderizer, sodium bicarbonate, boric acid, lemon juice, fresh water, steroid cream, alcohol, cold packs, papaya, or hydrogen peroxide will disable further stinging, and these substances may even hasten the release of venom. Heat packs have been proven for moderate pain relief if no vinegar is available. Pressure immobilization bandages, methylated spirits, or vodka should never be used for jelly stings. In severe Chironex fleckeri stings cardiac arrest can occur quickly, so cardiopulmonary resuscitation (CPR) can be life-saving and takes priority over all other treatment options.
In 2011, University of Hawaii Assistant Research Professor Angel Yanagihara announced that she had developed an effective treatment by "deconstructing" the venom contained in the box jellyfish tentacles. Its effectiveness was demonstrated in the PBS NOVA documentary Venom: Nature's Killer, originally shown on North American television in February 2012.
Wearing pantyhose or full body lycra suits during diving (both by women and men, also under scuba-diving suit) is an effective protection against box jellyfish stings. The pantyhose were formerly thought to work because of the length of the box jellyfish's stingers (nematocysts), but it is now known to be related to the way the stinger cells work. The stinging cells on a box jellyfish's tentacles are not triggered by touch, but are instead triggered by the chemicals found on skin.
As of 2007, at least 36 species of box jellyfish were known. These are grouped into two orders and seven families. A few new species have been described since then, and it is likely undescribed species remain.