The Curious Case of the Immortal Jellyfish

It's official: the only thing certain in this world is taxes. That's because death, for a tiny sea creature, is not inevitable. Turritopsis nutricul, a jellyfish-like hydrazoan, is the only animal known to be potentially immortal. Once it reaches sexual maturity, Turritopsis looks like a tiny, transparent, many-tentacled parachute (only about 5mm in diameter) that floats freely in warm ocean waters. But when times get tough, Turritopsis can turn into a blob, anchor itself to a surface, and undergo a sort of reverse methamorphosis back to its youthful form as a stalk-like polyp. That's like a butterfly turning back into a caterpillar. Scientists, who first described this phenomenon [pdf] in the 1990s, believe Turritopsis can repeat its life cycle indefinitely. The trick to Turritopsis' infinite do-overs is a process called transdifferentiation, which turns one type of cell into another. While other animals can undergo limited transdifferentiation to regenerate organs (salamandars ...