Chironex fleckeri, commonly known as the Australian box jelly and nicknamed the sea wasp, is a species of extremely venomous box jellyfish found in coastal waters from northern Australia and Papua New Guinea to Indonesia, East Timor, Cambodia, Malaysia, Singapore, the Philippines and Vietnam. It has been described as "the most lethal jellyfish in the world", with at least 64 known deaths in Australia from 1884 to 2021.
Notorious for its sting, C. fleckeri has tentacles up to long covered with millions of cnidocytes which, on contact, release microscopic darts delivering an extremely powerful venom. Being stung commonly results in excruciating pain, and if the sting area is significant, an untreated victim may die in two to five minutes. The amount of venom in one animal is said to be enough to kill 60 adult humans.
Taxonomy
Chironex fleckeri was named after North Queensland toxicologist and radiologist Doctor Hugo Flecker. On 20 January 1955, when a 5-year-old boy died after being stung in shallow water at Cardwell, North Queensland, Flecker found three types of jellyfish. One was an unidentified box-shaped jellyfish with groups of tentacles arising from each corner. Flecker sent it to Dr. Ronald Southcott in Adelaide, and on 29 December 1955, Southcott published his article introducing it as a new genus and species of lethal box jellyfish.
Description
thumb|Cnidocytes from Chironex fleckeri (400x magnification)
Chironex fleckeri is the largest of the cubozoans (collectively called box jellyfish), many of which may carry similarly toxic venom. Its bell usually reaches about in diameter but can grow up to . From each of the four corners of the bell trails a cluster of 15 tentacles. Black objects, on the other hand, cause them to move away. Their only known predators are green sea turtles and leatherback turtles, whose thick skin is impenetrable to the cnidocytes of the jellyfish, among other pelagic predators. This species has also been documented from the Philippines.
Sting
Chironex fleckeri is best known for its extremely powerful "sting". This sting can produce excruciating pain accompanied by an intense burning sensation, like being branded with a red hot iron. Stings may also result in white welts and lines that may be accompanied by blistering. In some cases, the sting can cause permanent damage or death to the skin and result in scars. Fatalities are most often caused by specimens of C. fleckeri that are larger than . If left untreated, large amounts of venom injection can cause fatality in 5 minutes. but most encounters appear to result only in mild envenomation. Among 225 analyzed C. fleckeri stings in Australia's Top End from 1991 to 2004, only 8% required hospital admission, 5% received antivenom and there was a single fatality (a 3-year-old child).
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 two to five minutes with an of 0.04 mg/kg. It has been postulated that a zinc compound could be developed as an antidote. Occasionally, swimmers who get stung will undergo cardiac arrest or drown before they can reach the shore or a boat.
In many cases, there will be a reaction that takes place days after the initial sting if the victim survives. This extremely itchy rash can last weeks after the initial sting. If the skin in the affected area is intact, certain creams and antihistamines may help to alleviate the symptoms. Signs like the one pictured are erected along the coast of North Queensland to warn people of such, and few people swim during this period. At popular swimming spots, net enclosures are placed in the water to allow people to swim while preventing jellyfish from entering.
thumb|left|200px|Box jellyfish warning signpost at a [[Cape Tribulation beach in Queensland, Australia]]
History of sting treatment
Until 2005, treatment involved using pressure immobilisation bandages, with the aim of preventing distribution of the venom through the lymph and blood circulatory systems. This treatment is no longer recommended by health authorities due to research that showed that using bandages to achieve tissue compression provoked nematocyst discharge.
The application of vinegar is a recommended treatment because vinegar (4–6% acetic acid) permanently deactivates undischarged nematocysts, preventing them from opening and releasing venom. A 2014 study demonstrated in vitro that while vinegar deactivates unfired nematocysts, there was also an increase in venom concentration in the solution, possibly by causing already-fired nematocysts (which still contain some venom) to release what remained. However, this study has been criticized on several methodological grounds, including that the experiment was done using a model membrane that is much different from (and more simple than) human skin. Also, the researchers did not determine whether the increase in venom concentration was caused by already-discharged nematocysts releasing more venom, or if the venom that was released initially had simply leaked back out through the membrane, thus confounding the concentration measurement. Despite these concerns, diluted acetic acid is still the recommended treatment. In 2019, the first antidote for Australian box jellyfish sting was discovered in Australia.
Reproduction
Chironex fleckeri is capable of both sexual and asexual reproduction and are oviparous.
Sexual Reproduction
A fully grown and sexually mature Chironex fleckeri medusa will begin trying to find a mate in the spring season. Usually, the jellies will move from their usual habitat to a freshwater river for this hunt. If a mate is located, sperm and eggs are expelled into the water by the male and female respectively to result in fertilization. The gametes produced by the spawning process will go on to become planulae and eventually small sea wasp polyps. They will use their two tentacles to hide away from predators by hooking onto a hidden surface and feeding on plankton. The parent organisms die shortly after reproduction occurs.