Ready for this jelly?

Jellyfish are simple creatures.

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NO BRAINER: They're made up of 95% water, with no brains, hearts or (often) eyes to complicate matters. They do have a mouth, though - it doubles as an anus - and a basic nervous system that lets them smell, detect light and respond to danger.

ENDLESS POSSIBILITIES: Your average jellyfish is here for a good time, not for a long time. Some only live for a few hours, while larger species can stick around for more than a year. Then there's the Turritopsis dohrnii, known as the "immortal jellyfish", which can technically live forever by reverting to a juvenile form.