Jellyfish have no brain, no heart, no bones, and no blood — and have survived 500 million years
Jellyfish have been on Earth for approximately 500–600 million years — predating sharks, trees, and dinosaurs. They have no centralised brain, no heart, no blood, no skeleton, and no respiratory system. They breathe by absorbing oxygen through their skin directly from the water. They 'think' using a distributed nerve net — a web of neurons with no centre. Despite this apparent simplicity, some jellyfish species display learning behaviour and navigate using light-sensitive eyes. One species — Turritopsis dohrnii — is considered biologically immortal, reverting to its juvenile state when stressed.
Jellyfish are defined by radical absence — no brain, no heart, no blood. That an animal with none of the organs we consider essential to survival has existed for 500 million years longer than most of the things we share a planet with makes 'essential' feel like a relative term.
“Jellyfish have no brain, heart, bones, or blood — and have survived 500 million years. One species reverts to its juvenile state when stressed and may be biologically immortal. 🪼 #OddlyHuman”