There is a type of jellyfish that can theoretically live forever. It can revert back to an adolescent stage after completing adulthood. It’s called “Immortal Jellyfish”.
They have no heart, brain, eyes or bones.
They have been around since before the age of dinosaurs.
Some are bioluminescent. This means they can produce their own light.
They have stinging cells on their tentacles that they use to paralyze animals to eat them.
They use their mouth to eat, discharge waste and shoot water out of to move themselves around.