Immortal Jelly Fish
The Turritopsis dohrnii are the only known animal capable of returning to a sexually immature state after having grown to sexual maturity. This makes these animals effectively biologically immortal. Putting aside the considerations of environmental stress, disease, and predators; these creatures could theoretically live forever.
Believed to have originated from the Pacific, this type of jellyfish hitches rides in passing ships’ ballast water. This allows them to rapidly spread across the world. Although theoretically immortal, most of these jelly fish succumb to disease in the wild. This has not stopped scientists from studying and testing them in laboratory environments with the goal of unlocking this amazing ability and using it in medicine and other scientific endeavors.