This Mysterious Sea Creature Is Immortal. Now Scientists Know Why

A strange, immortal tube-shaped animal has been discovered to regenerate a whole new body from only its mouth to avoid getting old.

This creature, named Hydractinia symbiolongicarpus, a tiny invertebrate that lives on the shells of crabs, is usually immune to aging altogether, but was found to use aging within its body to grow an entirely new body, a study published in the journal Cell Reports found.

"Studies like this that explore the biology of unusual organisms reveal both how universal many biological processes are and how much we have yet to understand about their functions, relationships and evolution," Charles Rotimi, co-author of the paper and director of the Intramural Research Program at the National Human Genome Research Institute (NHGRI), part of the National Institutes of Health, said in a statement. "Such findings have great potential for providing novel insights into human biology."

Hydractinia had previously been found to have special stem cells that it used for regenerating its tissues. These stem cells are capable of transforming—differentiating—into any type of body cell, which more specialized cells like heart tissue or muscle tissue cannot do. This makes them capable of growing new body parts; humans can only use stem cells during development, but animals like Hydractinia can use stem cells throughout their lifetimes, making them functionally immortal.

The researchers found that while Hydractinia stores its stem cells in the lower half of its body, but when they cut off its mouth, the mouth grew a whole new body, indicating that the animal could generate new stem cells. To investigate how these stem cells are triggered to generate, the authors described in the paper how they scanned the genome of Hydractinia for genes related to aging or "senescence"—lagging of cell repair and the aging of the body and its systems.

Here, they found that of Hydractinia's three senescence-related genes, one had been "switched on" in cells near the site of the mouth cut. When this gene was deleted from the genome, the animal could not regenerate, indicating that it needs senescence in order to regenerate new stem cells.

This is the opposite of the effect that senescence has on many other animals like humans.

"Most studies on senescence are related to chronic inflammation, cancer and age-related diseases," said Andy Baxevanis, study co-author and senior scientist at NHGRI. "Typically, in humans, senescent cells stay senescent, and these cells cause chronic inflammation and induce aging in adjacent cells. From animals like Hydractinia, we can learn about how senescence can be beneficial and expand our understanding of aging and healing."

Many animals are capable of this kind of tissue regeneration, including salamanders and axolotls.

"The ability to regenerate is actually very common in animals and widely distributed across the roughly 35 phyla (groups) of animals on Earth. Many of these groups are marine invertebrates that can have incredible regenerative abilities. Some of the more famous examples include sea anemones and flatworms, but there are many others (sea stars, acorn worms, mollusks, etc)," Heather Marlow, an assistant professor of organismal biology and anatomy at the University of Chicago, previously told Newsweek.

"They can do this by dedifferentiating existing cells and signaling to them to divide and differentiate into new tissues," Marlow said. "They can also do it by activating an existing resident population of stem cells that respond to signals of injury and divide to form the lost tissues. While it's unlikely that sea anemone or flatworm stem cells could be compared one on one to a human stem cell, the basic principles of how these stem cell populations are maintained, how they are activated and the genes they use to develop into the regenerated structures are important to study."

Some animals are even totally immune to aging, such as the hydra and the "immortal jellyfish" Turritopsis dohrnii.

The authors hope that this discovery in the Hydractinia may help us to understand aging in our own bodies, and how to combat the effects of senescence.

"We still don't understand how senescent cells trigger regeneration or how widespread this process is in the animal kingdom," said Baxevanis. "Fortunately, by studying some of our most distant animal relatives, we can start to unravel some of the secrets of regeneration and aging—secrets that may ultimately advance the field of regenerative medicine and the study of age-related diseases as well."

Do you have a tip on a science story that Newsweek should be covering? Do you have a question about aging? Let us know via science@newsweek.com.