Carukia barnesi is a small and extremely venom

Venom

Venom is the general term referring to any variety of toxins used by certain types of animals that inject it into their victims by the means of a bite or a sting...

ous jellyfish

Jellyfish

Jellyfish are free-swimming members of the phylum Cnidaria. Medusa is another word for jellyfish, and refers to any free-swimming jellyfish stages in the phylum Cnidaria...

 found near Australia

Australia

Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

. Stings can result in Irukandji syndrome

Irukandji syndrome

Irukandji syndrome is a condition that is induced by venomization through the sting of Carukia barnesi, a species of Irukandji jellyfish, and other cubozoans. The condition is rarely fatal, but if immediate medical action is not taken, within only 20 minutes the victim could go into cardiac arrest...

, and thus this species is commonly known as Irukandji jellyfish, although this name does not distinguish it from other Irukandji jellyfish

Irukandji jellyfish

Irukandji jellyfish are tiny and extremely venomous jellyfish that inhabit marine waters of Australia and which are able to fire their stingers into their victim, causing symptoms collectively known as Irukandji syndrome. Its size is roughly no larger than a cubic centimetre...

 such as Malo kingi

Malo kingi

Malo kingi is an Irukandji jellyfish named after victim Robert King, a tourist from the United States who died from its sting. It was first described to science in 2007, and is one of two species in genus Malo. It has some of the world's most potent venom, even though it is no bigger than a human...

.

A mature C. barnesi's bell is only 12 mm by 30 mm in height. It has four contractile tentacles, one extending from each bottom "corner" of its bell, ranging in length from 50mm to 500mm. The jellyfish was discovered by, and named after, Jack Barnes.