* Most jellyfish are harmless to human beings. But some are poisonous.
The sea wasp, or box jelly, is a deadly jellyfish found near Australia.
It's sting is more poisonous than the bite of any venomous snake. The tentacles of jellyfish are lined with stingers, which are like a self-contained firing mechanism. When it rubs against another creature, barbs called "nematocyst" shoot out like a harpoon, stinging its victim with venom. These stingers will keep firing until the creature stops moving.
* Scientists believe that jellyfish have been on our planet for more than 550 million years. Jellyfish are found in every ocean in the world and even in some freshwater lakes.
* The body of a jellyfish is made of a jelly-like substance called "mesoglea," that is sandwiched between two layers of cell lining. The outer layer of cells protects the jellyfish's body, and the inner layer makes up its stomach. A jellyfish has no control over its stingers. Even after it's dead, it can still inflict a painful sting.
* Jellyfishes can re-grow limbs and eyes. One type of jellyfish can even revert all of its cells to a young state (basically becoming a baby again, filled with stem cells) and re-grow entirely.