They can be bioluminescent, too, which means they produce their own light! Jellyfish have no brain, heart, bones or eyes. They are made up of a smooth, bag-like body and tentacles armed with tiny, stinging cells. These incredible invertebrates use their stinging tentacles to stun or paralyse prey before gobbling it up.br br Jellyfish are over 600 million years old. Before the dinosaurs, trees, or even fungi, there were jellyfish. br There could be 300,000 species of jellyfish.br They have no brain and are 98 water. br One species may be immortal.