It’s one thing to survive in harsh environments, but quite another to hit the reset button when faced with an imminent threat. Only one animal is known to have this remarkable ability: a small species of jellyfish, Turritopsis dohrnii, first discovered in the 1880s in the Mediterranean Sea and highlighted as a uniquely enduring organism in the exhibition Life at the Limits: Stories of Amazing Species.
Like all jellyfish, Turritopsis dohrnii begins life as a larva, called a planula, which develops from a fertilized egg. A planula swims at first, then settles on the sea floor and grows into a cylindrical colony of polyps. These ultimately spawn free-swimming, genetically identical medusae—the animals we recognize as jellyfish—which grow to adulthood in a matter of weeks.
Fully grown, Turritopsis dohrnii is only about 4.5 mm (0.18 inches) across, smaller than a pinky nail. A bright-red stomach is visible in the middle of its transparent bell, and the edges are lined with up to 90 white tentacles. These tiny, transparent creatures have an extraordinary survival skill, though. In response to physical damage or even starvation, they take a leap back in their development process, transforming back into a polyp. In a process that looks remarkably like immortality, the born-again polyp colony eventually buds and releases medusae that are genetically identical to the injured adult. In fact, since this phenomenon was first observed in the 1990s, the species has come to be called “the immortal jellyfish.”