Let's start with the oldest-living animal of all, and one of the
strangest in the entire animal kingdom: Turritopsis nutricula,
otherwise known as the immortal jellyfish. You might think that
this animal's common name is poetic, that perhaps it lives for a
few hundred years, impressing generations of scientists--but
you'd be wrong. Its name is literal: Turritopsis nutricula is
biologically immortal. The immortal jellyfish can theoretically
live forever, thanks to a process that is believed to be unique,
called transdifferentiation. It has the ability, at any stage in
its life, to completely transform back into a polyp, its
earliest stage of life. You can imagine it like the mythical
phoenix, an immortal bird which is repeatedly reborn as a chick.
The immortal jellyfish doesn't die; it merely regenerates its
cells in a younger stage, then ages naturally again. That
doesn't mean all Turritopsis nutricula are immortal; the species
is a small invertebrate in the ocean, and is susceptible to all
of the nasty thing