There is a species of jellyfish called Turritopsis dohrnii that is biologically immortal.
Here is how it works:
When most creatures get old, sick, or injured, they die. However, when this jellyfish faces physical trauma or environmental stress, it doesn't die—it "reboots." It undergoes a process called transdifferentiation, where its existing adult cells essentially transform back into youthful stem cells.
The jellyfish reverts from its floating adult form back into a polyp (a baby-like state attached to the seafloor), effectively starting its entire life cycle over again. It can repeat this process indefinitely, meaning it could theoretically live forever unless it is eaten by a predator or killed by a disease it can't escape.
Essentially, it is the only known animal that has found a way to "hit the reset button" on aging.
There is a phenomenon in the ocean called "The Milky Seas Effect," where massive patches of the ocean (sometimes the size of Vermont) glow with a steady, bright, milky light—so bright that they can be seen from space.
For centuries, sailors told tales of "glowing white waters," but scientists largely dismissed them as tall tales or simple bioluminescence from agitated plankton. However, in 2005, researchers used satellite data to confirm that these events are real.
Here is what makes it weird:
- It’s not triggered by movement: Most bioluminescence (like the kind you see on a beach) flashes only when the water is disturbed by waves or a boat. The Milky Sea glow is constant, steady, and uniform, lasting for days or weeks.
- It’s caused by bacteria, not plankton: The glow comes from a specific type of luminous bacteria (Vibrio harveyi).
- The "Quorum Sensing" mystery: A single bacterium isn’t bright enough to be seen. These bacteria only turn their lights on when they reach a certain population density. They essentially "talk" to each other using chemical signals, and once there are enough of them (trillions upon trillions), they all flip the switch at the exact same time to create a massive, glowing blanket.
Scientists still aren't entirely sure why they do this, though the leading theory is that they want to be eaten by fish so they can live more comfortably inside a warm gut.
There is a small, immortal species of jellyfish called Turritopsis dohrnii that can effectively hit the "reset button" on its own life.
When this jellyfish becomes injured, sick, or simply grows old, it doesn't die. Instead, it undergoes a process called transdifferentiation. Its cells transform back into their earliest states, and the jellyfish reverts from its adult form back into a polyp (a baby-like state).
It then settles on the ocean floor and starts its life cycle all over again. Theoretically, it can repeat this process indefinitely, making it biologically immortal.