The real story
In 1988 a marine-biology student, Christian Sommer, kept some tiny Turritopsis jellyfish in dishes on the Italian Riviera and noticed something odd: instead of dying, they seemed to vanish and come back as polyps. In 1996 Italian researchers including Ferdinando Boero confirmed it. Boero compared it to a butterfly turning back into a caterpillar.
The trick is called transdifferentiation. Over a day or three, the jellyfish's adult cells change identity and rebuild themselves as a polyp, which then buds off brand-new jellyfish. Labs have watched a single animal do this more than ten times. It isn't truly immortal: predators and disease still get it. And a few relatives, including another Turritopsis and a moon jelly, have since been caught doing something similar.
