Chironex fleckeri

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Chironex fleckeri is a highly venomous species of box jellyfish. Not a true jellyfish, it is a very fast swimmer and has very sophisticated eyes.

Chironex fleckeri grow to approximately the size of a basketball, is nearly transparent and has four clusters of 15 tentacles. When the jellyfish are swimming the tentacles contract so they are about 15cm long and as thick as bootlaces, when they are hunting the tentacles are thinner and about three metres long. The tentacles are covered with stinging cells or Nematocysts which are activated by pressure and a chemical trigger: they react to proteinous chemicals.

The polyps are found in estuaries in northern Australia, the medusa is pelagic and is found in the coastal waters of northern Australia and adjacent areas of the tropical Indo-West Pacific, and are also found in southeastern Asia. They are not usually found on the reef.

In common with other box jellyfish, Chironex fleckeri have four eye-clusters with twenty-four eyes. Some of these eyes seem capable of forming images, but it is debated whether they exhibit any object recognition or object tracking and it is not known how they process information from their sense of touch and eye-like light detecting structures. Chironex fleckeri live on a diet of prawns and small fish and are themselves prey to turtles.

Box Jellyfish warning signpost at a Cape Tribulation beach in Queensland, Australia. (click to [enlarge]).

Chironex flickeri appear to avoid human beings when they are close to them and so can be said to avoid stinging humans. Their sting is incredibly powerful and can be fatal. The sting produces instant excruciating pain accompanied by an intense burning sensation, and the venom has multiple effects attacking the nervous system, heart and skin at the same time. While an appreciable amount of venom (about ten feet or three metres of tentacle) needs to be delivered in order to have a fatal effect on an adult human, the potently neurotoxic venom is extremely quick to act. Fatalities have been observed as little as four minutes after envenomation, notably quicker than any snake, insect or spider and prompting its description as the world's deadliest venomous animal. Although an antivenom exists, treating a patient in time can be difficult or impossible. Dousing a sting with vinegar immediately kills any venom which has not been activated, while rubbing a sting exacerbates the problem. Estimates vary, but it is thought that Chironex fleckeri has killed about one hundred people in Australia over the last one hundred years, making it possibly the most dangerous species of jellyfish in the world.

External links

• [Chironex fleckeri on oceanfootage.com]
• [Chironex fleckeri on fccj.org]
• [Chironex fleckeri on an Apopka High School webpage by Ted Klenk]

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