Jellyfish canal. Cilia in these canals circulate the fluid in a regular direction. The box jellyfish is largely similar in structure. It has a squarish, box-like bell from each of the four lower corners of which hang a short pedalium or stalk which bears one or more long, slender tentacles. The rim of the bell is folded inwards to form a shelf known as a velarium which restricts the bell's aperture and creates a powerful jet when the bell pulsates, allowing box jellyfish to swim faster than true jellyfish. Hydrozoans are also similar, usually with just four tentacles at the edge
Irukandji jellyfish fatal, but two people in Australia are believed to have died from Irukandji stings in 2002 during a rash of incidents on Australia's northern coast attributed to these jellyfish—greatly increasing public awareness of Irukandji syndrome. It is unknown how many other deaths from Irukandji syndrome have been wrongly attributed to other causes. It is also unknown which jellyfish species can cause Irukandji syndrome apart from "Carukia barnesi" and "Malo kingi". Irukandji jellyfish Irukandji jellyfish ( ) are any of several similar, extremely venomous species of box jellyfish. With an adult size of roughly a cubic centimetre (1 cm), they are