With a very small adult size of about a cubic centimetre (1 cm3), they are both the smallest and one of the most venomous jellyfish in the world. Robert Drewe

With a very small adult size of about a cubic centimetre (1 cm3), they are both the smallest and one of the most venomous jellyfish in the world. Robert Drewe describes the Irukandji jellyfish sting as "100 times as potent as that of a cobra and 1,000 times stronger than a tarantula's". Irukandji jellyfish's stings are so severe they can cause fatal brain hemorrhages and on average send 50-100 people to the hospital annually. https://en.m.wikipedia.org/wiki/Irukandji_jellyfish https://en.m.wikipedia.org/wiki/Irukandji_jellyfish