The sea creature that refuses to die

In the vast, mysterious depths of the ocean, there lives a creature that seems to defy one of life’s most fundamental rules: that all living things must eventually die. Meet Turritopsis dohrnii, better known as the immortal jellyfish—a translucent, fingernail-sized marvel that appears to reverse its biological clock, again and again, without limit.

First described in the late 19th century but only understood in the 1980s, this tiny hydrozoan has captivated biologists, geneticists, and philosophers alike. Could this humble sea creature hold the secret to halting—or even reversing—aging?

A life rewritten in reverse

Like most jellyfish, Turritopsis dohrnii begins life as a fertilized egg that becomes a free-swimming larva. Eventually, it anchors to a surface and transforms into a polyp—an anemone-like stage that buds off into adult medusae, the classic jellyfish form. For most species, the medusa is the final stage before death. But when this jellyfish is stressed, injured, or starving, something astonishing happens.

Rather than die, the medusa begins to revert. It shrinks, absorbs its own tentacles, and collapses into a blob, eventually transforming back into a polyp. This process, called transdifferentiation, involves mature cells reprogramming into other cell types—a biological reboot. From this regenerated polyp, new jellyfish emerge, genetically identical to the original.

In ideal conditions, this cycle can repeat indefinitely, making T. dohrnii the only known animal capable of true biological immortality.

An accidental discovery, a lasting fascination

This extraordinary ability was discovered by accident. In the 1980s, marine biology students Christian Sommer and Giorgio Bavestrello were studying jellyfish off the Italian coast when they noticed something strange: mature jellyfish transforming back into polyps without reproducing. What they observed challenged the traditional view of a linear life cycle.

Although the scientific community didn’t immediately grasp the magnitude of the discovery, further research confirmed what Sommer saw—T. dohrnii was capable of rejuvenation on demand.

Japanese scientist Shin Kubota, based at Kyoto University’s Seto Marine Biological Laboratory, has since become the jellyfish’s most devoted caretaker. For over two decades, he’s kept colonies of T. dohrnii alive in his lab, meticulously feeding them and documenting their seemingly endless regenerative loops.

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The science behind reversal

Recent genomic studies have begun to unravel the mechanics of this biological phenomenon. Scientists have identified a suite of genes in T. dohrnii that play critical roles in DNA repair, pluripotency (the ability for cells to become any type of tissue), and cellular reprogramming.

Under stress, adult jellyfish activate these genes in a way that essentially rewinds their biological clocks. Unlike other jellyfish that might regenerate once under specific conditions, T. dohrnii appears to have refined the process into a survival mechanism.

Researchers caution, however, that this isn’t “immortality” in the absolute sense. These jellyfish can still be eaten by predators, succumb to disease, or die from environmental changes. But their ability to reset their aging process remains biologically unprecedented.

The silent spread of an immortal species

Originating in the Mediterranean Sea, T. dohrnii has now been found in oceans around the globe. It likely hitchhiked aboard ships, surviving in ballast water thanks to its ability to rejuvenate when under duress. Unlike other invasive species that disrupt ecosystems, this jellyfish has no known environmental impact—at least not yet.

Its spread, however, is a subtle reminder of humanity’s far-reaching influence on marine ecosystems and the hidden travelers we unknowingly transport.

What this means for us

For all its wonder, the immortal jellyfish remains a biological outlier. Researchers like Maria Pascual Torner, who studies the species’ genetics, emphasize that while it offers valuable insights into regeneration and aging, human immortality is still a myth.

Our bodies rely on tightly regulated cycles of cell death and renewal. If every cell pursued immortality, as cancer cells do, the system would collapse. “Systems need entries and exits,” Pascual Torner says. Death, paradoxically, is essential for life as we know it.

Still, understanding how T. dohrnii controls cell identity, DNA repair, and regeneration could help advance regenerative medicine. Already, the concept of cellular reprogramming is at the heart of stem cell research. Learning how this jellyfish resets its own cells might one day improve how we heal organs, treat degenerative diseases, or slow the cellular damage of aging.

Conclusion

In the end, the immortal jellyfish may not make us live forever. But it does offer something perhaps even more valuable: a reminder that nature still holds mysteries we’ve only just begun to explore. In the smallest, most delicate creatures, we may find the keys not to immortality—but to aging more gracefully, more healthfully, and with more wonder at the biological marvels all around us.