The Turritopsis dohrnii jellyfish is thought to be immortal, since it can transform back into a colony of polyps (individual organisms). As the jelly ages, it eventually settles onto the sea floor and becomes polyps. The polyps then spawn new, genetically identical jellyfish.

If a Turritopsis dohrnii gets physically harmed or starts to starve, it can transform back into a polyp at will — then in turn produce new, genetically identical jellyfish.