It began as a fortuitous observation in a seawater tank.
A small piece of sea cucumber left behind from a laboratory experiment should have begun degrading within days.
Instead, weeks passed, then months, and eventually years.
The tissue was not only still present. It was alive.
Now, a study led by PhD student Sara Jobson in Memorial University’s Department of Ocean Sciences in the Faculty of Science, has documented what may be the first known case of long-term tissue survival and growth outside a living organism under natural conditions — a discovery that raises new questions about life, death and the boundaries in between.
“We’re seeing something that hasn’t been documented before in this kind of environment,” said Ms. Jobson, who led the research team in Dr. Annie Mercier’s lab at the Ocean Sciences Centre in Logy Bay, N.L. “We’ve always known that sea cucumbers can regenerate remarkably well, but the assumption was that any detached tissue would simply die.”
That assumption proved wrong.
Published in Science Advances, the research focuses on Psolus fabricii, a cold-water sea cucumber native to the North Atlantic.
When fragments of the animal’s tissue were removed and placed in flowing natural seawater, they healed, re-organized and continued to function for over three years.
Rethinking what it means to be alive
Scientists have long understood that sea cucumbers and other echinoderms possess remarkable regenerative abilities.
Entire organs can be regrown after injury, and lost body parts can be replaced.
What had never been observed until now was the fate of the tissue left behind.
“They challenge our usual definitions — they’re not clearly alive in the traditional sense, but they’re not dead, either.”
Conventional wisdom holds that complex tissue quickly decays once separated, and even cell lines kept in laboratory settings typically require tightly controlled conditions to survive.
But the research team found something entirely different.
Their samples were kept in non-sterile seawater: a microbially rich environment where tissue would normally break down.
Instead, it thrived.
“These fragments aren’t developing into new individuals, but they are continuing to function as self-sustaining biological units,” Ms. Jobson said. “They’re maintaining active cellular processes even though they’re no longer part of the original organism.”
Fragments taken from tube feet and tentacles not only survived but actively repaired themselves.
Wounds closed within days, cells continued to divide and reorganize, and the tissue showed signs of immune activity and metabolic function.
Without a mouth or digestive system, the fragments appeared to sustain themselves by absorbing dissolved nutrients directly from seawater and possibly recycling their own internal resources.
“They challenge our usual definitions — they’re not clearly alive in the traditional sense, but they’re not dead either.”
The researchers have informally dubbed them “zombie tissues,” reflecting their unusual state between life and death.
They do not develop into new organisms, nor do they reproduce.
Yet they persist, functioning as independent living systems.
A discovery years in the making
The finding was not the result of a single experiment, but of careful observation over time.
The team first noticed that some excised tissue had not decayed after several weeks.
Intrigued, they extended their monitoring and the tissue kept going.
Eventually, Ms. Jobson initiated the formal study that was recently published.
Over the course of more than three years, researchers tracked changes in the samples, documenting growth, structural reorganization and sustained biological activity.
Even at the end of the study period, there were no clear signs of aging or decline.
“Our findings generate so many other questions,” said Ms. Jobson. “Why would these small tissue chunks maintain the ability to heal and survive without any reproductive purpose? What’s the evolutionary driver that allows that to happen?”
Comparative experiments with other echinoderms, including sea stars and sea urchins, did not produce the same results.
Those tissues degraded within weeks or months, highlighting the unique properties of Psolus fabricii.
Implications for science and medicine
While the notion of “immortality” is still debated and may not fully apply, the implications of this work are far-reaching.
For centuries, scientists have attempted to grow and maintain living tissue outside an organism.
Successes such as immortal cell lines require highly controlled laboratory environments and typically involve simplified systems, not complex, multicellular tissue capable of healing and organizing itself.
The sea cucumber tissues, by contrast, demonstrate the ability to persist in natural conditions while maintaining structure and function, a combination not seen before.
This opens new possibilities for regenerative biology, tissue engineering and biomedical research.
“From everything we’ve seen so far, there’s no indication that these tissues are approaching an endpoint.”
These “living explants” could provide a model system that is easier to maintain, ethically less complex and potentially more reflective of real-world biological conditions without sacrificing the donor animals.
“We still don’t understand what evolutionary advantage might explain this kind of persistence,” Ms. Jobson said.
She compares the phenomenon to a detached body part that continues to heal and function independently.
“From everything we’ve seen so far, there’s no indication that these tissues are approaching an endpoint.”
There are still many unanswered questions.
For now, the discovery underscores the importance of curiosity-driven research and of paying attention when something in a tank does the unexpected.
What began as a simple observation has opened a new window into the resilience of life in the ocean and perhaps, one day, into new ways of understanding our own.
