Turritopsis Jellyfish Is Biologically Immortal

While most organisms follow a one-way path from birth to death, a tiny jellyfish in our oceans possesses a biological reset button. The "immortal jellyfish," or *Turritopsis dohrnii*, cheats death from old age or injury by reversing its own development. When faced with environmental stress or physical harm, an adult medusa can settle on the seafloor, where its body essentially melts into a cyst-like blob. From this blob, a new polyp colony emerges, which is the stationary, juvenile stage of the jellyfish life cycle. This new colony then buds off genetically identical medusae, allowing the jellyfish to begin its life anew.

The secret to this remarkable feat is a cellular process called transdifferentiation. This allows specialized adult cells, like those in its bell or tentacles, to reprogram themselves into entirely different types of cells to form the new polyp. This cellular flexibility is incredibly rare in the animal kingdom and is a major focus of research in regenerative medicine. For most animals, including humans, cell development is a one-way street; a mature heart cell cannot simply decide to become a skin cell.

Despite this potential for eternal life, the immortal jellyfish is not invincible. Its discovery was a scientific accident in the 1990s when a forgotten lab sample was observed reverting its life cycle. In the wild, however, these tiny creatures are vulnerable to predation and disease. Most meet a conventional end in the stomach of a larger animal long before they have a chance to grow old and reverse their life cycle.