IMMORTAL JELLYFISH

This Jellyfish has the ability to "reverse" age. It can make itself age backwards to before sexual maturity. Based on what science knows about this cellular change, this jellyfish could do this infinitely, rendering it "IMMORTAL". Science calls this "Biological Immortality". However this doesn't mean it lives forever. The jellyfish is still prey for other animals like sharks, and can fall to disease.
For those that think immortality isn't natural. Here is one version and case of it being so.