Box jellyfish - San Francisco Chronicle (blog)

The Box jellyfish (Chironex fleckeri) is found during the summer months in the coastal waters of northern Australia, from Gladstone in Queensland to Broome in Western Australia, but not on the Great Barrier Reef. It is the most dangerous jellyfish and indeed one of the most dangerous venomous creatures in the world. It is large, weighing up to 6 kg and measuring about 20-30 cm across the bell. The tentacles may stretch up to 2 metres. It is transparent in the water, and therefore difficult to see. It has 4 bundles of tentacles, which may number up to 60 in total. Each tentacle contains many millions of nematocysts or stinging cells which discharge venom through the skin on contact. Contact with a large amount of tentacular material over a wide surface area can result in massive envenomation. Most stings occur in the summer months in shallow water near the beach, and are particularly common in children. (In two case series the average age of box jellyfish sting victims was 14 years with a median age of 11 years.)