A species of jellyfish called Turritopsis dohrnii can revert its adult cells back to a juvenile polyp stage when injured or starving, effectively restarting its... (opens in new tab)

The tiny jellyfish Turritopsis dohrnii can reorganise its adult cells back into a juvenile polyp when stressed, restarting its life cycle indefinitely. Biologists have observed more than ten reversals in a single animal and have yet to find any limit.