Box jellyfish (class Cubozoa) are cnidarian invertebrates distinguished by their cube-shaped medusae. Chironex fleckeri, Carukia barnesi and Malo kingi are highly venomous creatures. Stings from these and a few other species in the class are extremely painful and sometimes fatal to humans.
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. Where as 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. They therefore have 24 eyes. A box jellyfish has the closest thing a known jellyfish has to a brain. Tests have shown that they have a limited memory, and have a limited ability to learn.
The tentacles of some species can reach up to 3 metres in length. Box jellyfish can weigh up to 2 kg. 
Although the venomous species of box jellies are largely, or entirely, restricted to the tropical Indo-Pacific, various species of box jellies 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).
Defense and feeding mechanisms
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 it is used to catch prey (small fish and invertebrates, including shrimp and bait fish) and for defense 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.
Danger to humans
Although the box jellyfish can be 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 postulates 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 hence 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.
Treatment of stings
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.
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. Pressure immobilization bandages, methylated spirits, or vodka should never be used for jelly stings.
In 2011, University of Hawaii Assistant Research Professor Angel Yanagihara announced that she had developed an antivenom 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.
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.
- Order Carybdeida
- Order Chirodropida
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- Cubozoa classification
- ThinkQuest: Box jellyfish, Boxfish, Deadly sea wasp
- Box Jellyfish – Jellyfish Facts
- Box Jelly Fish, dangers on the great barrier reef
- Jellyfish eyes
- Jellyfish Predictions Waikiki, Hawai'i
- Box Jellyfish by an Australian toxicologist
- Daily Telegraph
- Box Jellyfish | Smithsonian's Ocean Portal
- Box Jellyfish images
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