The way it works, to our understanding, is these immortal Jellyfish his sexual maturity and have offspring, or another for of stress (starvation, temperature ch

The way it works, to our understanding, is these immortal Jellyfish his sexual maturity and have offspring, or another for of stress (starvation, temperature change, attack, etc...) and they revert from sexual maturity to a polyp stage and restart the life cycle, and unless they are killed they continue this cycle in perpetuity. Unfortunately we can't age these Jelly fish or even confirm they have undergone the reversion transformation process (except under lab observation). So while I am not saying yes, a single jelly fish has lived the entire 500 million years, its certainly possible and the idea behind biological immortality. Maybe one day we can figure out a way to age them and find some older than the dinosaurs.