Chironex fleckeri

The deadly sea-wasp box jellyfish

A book I received one day from an anonymous benefactor contained a collection of true “horror stories”, namely the medical reports for the coroner of thoroughly documented human fatalities in Australia, caused by marine invertebrates. Now, while scorpions, funnel web and red back spiders are infamous enough and perhaps will feature on their own one day in this column, poisonous jellyfish, most notably the so-called sea-wasps and their fiendish deeds are far less known. Possibly the most potently venomous animals in the world are the Australian cubomedusan box jellyfish Chironex fleckeri and its smaller relative the Irukandji jellyfish Carukia barnesi. Measuring not even 1 cm across its bell and with tentacles less than a metre long, the Irukandji jellyfish may be small, but it can be a killer and its venom has been credited with a power 100 times more potent than that of a cobra.

With a body length of 5 cm and roughly matchbox size, Chironex fleckeri is not exactly a giant amongst the jellyfishes, but its tentacles can reach a metre and more. Unfortunately, the body of this jellyfish is rather transparent and so are its numerous and dangerous tentacles. Like other jellyfish species the box jellies possess specialized nettle cells on their tentacles, but unlike the majority of jellyfishes, whose stingers have little effect on the human skin and may cause no more than a bit of burning and reddening, the ones belonging to Chironex fleckeri and Carukia barnesi don’t just burn: they kill. Another difference: box jellies have eyes with lenses and a retina, but how much and what they can see with them (and how they can process the information with no brain and only a nerve net) are questions still being investigated. Their nettle cells are hollow little cysts in which a coiled whip-like flagellum with barbs and stilettes rests under extreme pressure, ready to shoot out when released through contact and a chemical stimulus, for example, with a bather’s or fisherman’s skin. The release of the venomous flagellum takes only 3/1000 of a second and once anchored in the skin the 0.5 mm long tube breaks and releases its poison. Trying to rub off the rubbery tentacles will often lead only to more nettle cells releasing their poison.

Nobody knows how many of these chemically charged darts the sea wasps can release, but even the totally harmless (for humans, but not for waterfleas) freshwater polyp Hydra has no less than 50,000 of this powerful contact weapons. Once in a human, the poison of these jellyfish has a devastatingly rapid effect. My book has this to report about a healthy 38 year old man: from the time he was stung near Townsville in northern Queensland (a notoriously dangerous spot) to when he appeared to pass away no more than about 10 minutes had passed. The autopsy revealed numerous extensive weals of purplish colour on the legs extending to the right foot, minute haemorrhage into cerebral hemispheres, acute pulmonary oedemata in both lungs and acute venous congestion in liver and kidneys. And why are these jellyfish so enormously poisonous? Because they are small and weak and feed on prey that is fast and much stronger than they themselves are. They therefore need a poison that more or less instantaneously incapacitates their prey. Unfortunately these jellyfish are most common during the Australian summer tourist season around Christmas, at a time when people head to the beaches. Sadly evolution has not taught the jellyfish that human beings don’t really belong to their food spectrum.

jellyfish lighter cigarette fire

Not the same as these ones!

© Dr V.B. Meyer-Rochow and, 2017.
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