The turritopsis nutricula species of jellyfish may be the only animal in the world to have truly discovered the fountain of youth.

Since it is capable of cycling from a mature adult stage to an immature polyp stage and back again, there may be no natural limit to its life span. Scientists say the hydrozoan jellyfish is the only known animal that can repeatedly turn back the hands of time and revert to its polyp state (its first stage of life).

It's a Metroid.