Meet The Immortal Jellyfish That Can Reverse Its Own Aging Process — A Biologist Explains

InnovationScienceMeet The Immortal Jellyfish That Can Reverse Its Own Aging Process — A Biologist ExplainsByScott Travers,Contributor.Forbes contributors publish independent expert analyses and insights. I write about biodiversity and the hidden quirks of the natural world.Follow AuthorMay 26, 2026, 08:30am EDTJellyfish have repeatedly riddled the world of marine biology with its toughest mysteries. The immortal jellyfish might be the biggest one so far.gettyAging is biology’s most reliable law. Every organism that has ever lived, from the oldest known tree to the longest-lived vertebrate on record, has obeyed it. Cells accumulate damage. Tissues lose function. Death eventually follows. The universality of this process is so complete that biologists have spent decades not asking whether aging can be stopped, but simply trying to understand why it happens at all. The immortal jellyfish (Turritopsis dohrnii), however, raises the former once again.Smaller than the nail on your little finger, about 4.5 millimeters (0.17 inches) across, this transparent hydrozoan drifts through the world’s oceans with a bright red stomach visible through its belly and up to 90 tentacles trailing behind it. It’s easy to miss, and for most of the 20th century, science did. But T. dohrnii possesses something that no other animal on Earth is known to possess: the ability to reverse its own biological age. Not slow it. Not pause it. Reverse it — repeatedly, and apparently without limit.It’s the only known metazoan capable of doing this. And the more closely scientists have looked at how, the more it has begun to challenge assumptions about what aging actually is.How Does The Immortal Jellyfish Hit Reset?To understand what makes T. dohrnii extraordinary, it helps to understand what it shares with every other jellyfish. Like all hydrozoans, it begins life as a microscopic planula larva, drifting briefly in open water before settling on the seafloor and developing into a colonial polyp — a small...