Which is the world's most dangerous jellyfish?

The Irukandji jellyfish and the box jellyfish are the most dangerous jellyfish in the world. The box jellyfish lives in Australia. If they sting you, you can die anywhere between one and two days. Some of the most dangerous jellyfish are found off the coast of Brazil. Box jellyfish venom is the most lethal in the animal kingdom. There are many tentacles which are harpoon-shaped needles that inject venom into the victim. Some species of box jellyfish manufacture extremely potent venom.

The box jellyfish's nervous system is developed more than that of many other jellyfish, and they have a nerve ring wound the base of the bell that coordinates their pulsing movements. The box jellyfish can move more rapidly than any other jellyfish.