Spanish explorer Juan Ponce de Leon sought in vain for the Fountain of Youth that would confer eternal life. Modern researchers think humans may some day live as much as 500 years. (Bowhead whales in the Arctic have been documented to live for more than a century.) Heck, there's even a new film out about one man's quest to live forever.
It appears that Turritopsis nutricula may indeed be Earth's only immortal creature. (Note: The photo features a similar hydrozoan jelly, the giant bell jelly, Scrippsia pacifica.)
The key lies in T. nutricula's life cycle, which (as with other jellies) is quite different from the stages of most other animals. Jellies exist both as free-swimming adult medusae -- the versions with tentacles that we're familiar with -- and as anemone-like polyps, stalked creatures like jellies' anemone and coral relatives.
Apparently T. nutricula can reverse the process -- changing back to the immature polyp stage after growing into the adult medusa. (Hence the potential for immortality.)
So....what do you think?