There are actually two species of Jellyfish (Carukia barnesi and the recently discovered Malo kingi) - and they are thought to be the most venomous creatures in the world.
Their bite is definitely bigger than their bark - its size is roughly no larger than a cubic centimetre (1 cm³) and yet its venom is very powerful, 100 times as potent as that of a cobra and 1,000 times as potent as that of a tarantula.
The Irukandji are unique from other jellies in two prominent ways: they have stingers on their ‘bell’ as well as their tentacles, and they have the ability to fire stingers from the tips and inject venom.
Irukandji jellyfish were at one time thought to be in the northern waters of Australia only. Since then, according to a National Geographic documentary on jellyfish, the species has been found in waters as far north as the British Isles, Japan, the Florida coast of the United States.