Sea Cucumber Tissues That Don't Die Even When Detached: The "Zombies of the Sea" Challenge the Boundaries of Life

What does it mean to be "alive"?

Is it the beating of a heart? The ability to absorb nutrients? The capacity to heal wounds? The response to stimuli? Or perhaps the ability to grow and reproduce as an individual? We usually refer to these conditions collectively as "life." However, research on a certain sea cucumber living in the North Atlantic is shaking these boundaries from an unexpected direction.

The focus this time is on a species of sea cucumber called Psolus fabricii, which inhabits cold seas. Researchers have confirmed that small tissue fragments detached from this sea cucumber continue to live for years in a natural seawater environment, despite being in a state that would typically lead to death and decomposition. Moreover, these tissues did more than just maintain their shape. They sealed wounds, continued cellular activities, absorbed nutrients, and responded to stimuli.

The research team describes this phenomenon as "tissue immortality under natural conditions." It's a strong term, but it also needs to be taken cautiously. The "immortality" referred to here is not the eternal life seen in myths or science fiction. It is a scientific expression indicating that during the observation period, the tissues showed no clear deterioration or necrosis and maintained their function over the long term.

Still, the reason this discovery is being met with astonishment is clear. Complex tissues detached from the body usually cannot survive independently for long. They lack blood flow. They don't have the integrated system of nerves, immunity, and nutrient supply that the whole organism provides. Moreover, the tissue fragments in this study were maintained not in a strictly controlled sterile culture device but in natural seawater containing bacteria and microorganisms. This is quite an unusual phenomenon from the perspective of conventional biology.

The trigger was a "foot" left behind by chance

The discovery did not begin with a planned large-scale experiment. Rather, it started with a small sense of discomfort in the laboratory.

Psolus fabricii firmly attaches itself to rocks and the walls of tanks. When researchers remove an individual from a tank, small foot-like tissues called tube feet sometimes remain on the glass surface. For sea cucumbers, detaching a part of their body is not an unusual phenomenon. Many organisms have the ability to lose and later regenerate parts of their body when attacked by predators or under severe stress.

However, the remaining tube feet did not disappear after a few days or even weeks. Instead of rotting and disintegrating, they appeared to heal their wounds and slightly grow. Continued observation showed that the tissue fragments survived for months and even years.

As an additional experiment, researchers examined tissue fragments derived not only from the tube feet but also from the main body and tentacles. The results were equally puzzling. Despite lacking a mouth or intestines, the tissues absorbed amino acids dissolved in seawater. Signs of immune activity were observed, and cell proliferation and tissue reorganization were confirmed. Some even responded when poked from the outside.

It was as if, after being separated from the individual, the tissues themselves switched to a "self-maintenance mode."

Not "Regeneration," but "Something Other Than an Individual"

The important point here is that these tissue fragments did not grow into a new sea cucumber.

In the biological world, there are examples of new individuals regenerating from parts of the body. Planarians are famous for their ability to regenerate even when cut into small pieces, and starfish and some sea cucumbers are known for their high regenerative abilities. Some species of sea cucumbers even split their bodies to multiply into two individuals.

However, the tissue fragments of Psolus fabricii did not develop into complete individuals within the observed range. In other words, this is not simple "asexual reproduction." Nor are they dead tissues. This is why researchers jokingly refer to them as "zombies."

They are not individuals. They do not reproduce. Yet, they are not dead. Cells work, tissues heal wounds, and they obtain nutrients from the environment. In conventional classifications, they are very difficult to categorize.

This very point is what makes this discovery more than just a piece of bizarre creature news. If life is considered from an "individual" perspective, these tissue fragments appear to be incomplete beings. However, if life is viewed as a "localized system that maintains itself," there is indeed a living system present.

Why Can Sea Cucumber Tissues Survive?

Although no definitive answer has been reached, several possibilities are being considered.

First, echinoderms, including sea cucumbers, are known for their high regenerative abilities. Starfish, sea urchins, and sea cucumbers are known for their ability to regenerate lost arms and tissues. Since Psolus fabricii can regenerate tube feet and tentacles, it is possible that the mechanism for sealing wounds and maintaining cells is highly developed.

However, the current phenomenon differs in that it is not "the main body regenerating lost parts," but rather "the lost tissue fragments maintaining themselves." To use the example of a lizard detaching its tail to escape, normally the main body would only grow a new tail. What is happening with this sea cucumber is akin to the detached tail healing its wounds, absorbing nutrients, and continuing to live for years.

Another key is the ability to survive in natural seawater. Usually, maintaining cells or tissues outside the body requires sterile conditions, nutrient media, and temperature control. However, the sea cucumber tissues did not disintegrate in natural seawater containing microorganisms. This suggests they might possess some immune or chemical defense mechanisms to prevent infection and decay.

Some explanations touch on the possibility that specific chemical substances unique to Psolus fabricii protect the tissues from bacteria. However, this is a hypothesis that requires further verification, and it is not yet at a stage where it can be definitively stated that "this substance is the secret to immortality."

Ethical Implications Highlighted by Comparison with HeLa Cells

A frequent comparison in this study is with HeLa cells. HeLa cells originate from cervical cancer tissue taken from a woman named Henrietta Lacks in 1951. They have the property of being able to proliferate indefinitely and have made significant contributions to modern medicine, including cancer research, virus research, and drug development.

However, HeLa cells also carry serious ethical issues. The cells were taken without the individual's full consent and have been used in research worldwide for many years. HeLa cells have become a symbolic presence when considering the development of life sciences and issues of patient rights and consent.

The tissue fragments of Psolus fabricii are noteworthy because they might partially avoid such ethical and practical challenges. Of course, ethics are necessary in animal research as well, but they can be handled within a different framework than human-derived cells. Additionally, if they can be maintained long-term under relatively simple conditions like natural seawater, they could become a useful model for studying aging, wound healing, toxicity testing, and environmental stress.

For example, they could be applied in experiments investigating how rising seawater temperatures, pathogens, and pollutants affect tissues. The unknown resistance and repair mechanisms possessed by marine organisms could provide clues not only for medicine but also for understanding changes in the marine environment.

On Social Media, It's a Buzz as "Real Zombies" and "The Definition of Life is Breaking"

This news has elicited strong reactions on social media.

On X, posts introducing the research content prominently feature expressions like "real zombies" and "beings on the boundary of life and death." Many are astonished by the fact that the detached tissues have continued to live for over three years and absorb amino acids from natural seawater. In the Japanese-speaking world, introductions like "apparently absorbing amino acids from the surrounding seawater" have spread, being received for both their eerie sci-fi nature and biological intrigue.

In the English-speaking world, there are reactions expressing expectations for research applications, such as "Could this become a new model for ethical aging research?" and "There are still unknown biological functions sleeping in the sea." Even in the official post by Science Advances, the potential for applications in regenerative biology and aging research is emphasized, highlighting the significance of this as more than just a peculiar biological news story.

On the other hand, on Reddit, there were comments reacting to the expression "humanely excised." This phrase, meaning "humanely removed" for research purposes, might sound somewhat strange in the context of handling sea cucumber tissues. The mix of the seriousness typical of scientific news and the impact of the term "zombie tissues" has resulted in a reader response that is half surprise and half bewilderment.

Moreover, there is a need for cautious views against the leap in expectations, such as "Will this make humans immortal?" What has been confirmed this time is the phenomenon of a type of sea cucumber tissue fragment surviving long-term under special conditions, and it does not immediately lead to the creation of technology to rejuvenate human organs or bodies. On social media, the word "immortality" tends to take on a life of its own during the process of becoming a topic, but researchers and experts are urging a limited interpretation of its meaning.

Experts Are Cautious About the Word "Immortality"

In expert comments published by the Science Media Centre Spain, the research itself is evaluated as solid and well-designed. However, it is pointed out that caution is needed with the expression "immortality."

The fact that no deterioration or necrosis was observed during the observation period is very important. However, it does not prove that they "will never die." In the future, it will be necessary to investigate whether cellular aging is truly not occurring, as well as DNA and chromosomal structures, the limits of cell division, and the accumulation of long-term mutations.

Additionally, it is important to determine whether this phenomenon is unique to Psolus fabricii, whether it is also seen in closely related species, and in which tissues it occurs most strongly. If this ability is limited to specific species, it raises the question of why that species evolved such a mechanism. Conversely, if similar phenomena are found in other echinoderms, it might suggest that a broader "tissue maintenance ability" exists in marine organisms that has been overlooked until now.

Is Life Not Complete with Just the "Individual"?

What makes this discovery philosophically interesting is that it prompts a reconsideration of the unit of life.

We usually view organisms as individuals. A sea cucumber is one sea cucumber, a human is one person. We understand life within the flow of an individual taking in nutrients, growing, aging, reproducing, and dying.

However, the tissue fragments of Psolus fabricii maintained a certain degree of autonomy even when separated from the individual. Of course, they have no brain, do not reproduce, and are not complete individuals. Yet, they heal wounds, metabolize, and respond to the environment. This shows that parts of the body can maintain themselves as "localized life systems" more than expected.

One expert explains that normal tissues can only live with the support of the whole organism, including blood flow, immunity, nutrition, signaling molecules, and waste removal. The sea cucumber tissues in this study challenge that premise. Are tissues merely subordinate parts of the individual? Or, under certain conditions, can they become small life units that maintain themselves?

This question also connects to regenerative medicine and tissue engineering. When considering artificial organs, transplant tissues, and cell models maintained outside the body, understanding how tissues maintain themselves, prevent infection, and delay aging is extremely important. The sea cucumber tissue fragments might be an example of nature already implementing that mechanism.

It Doesn't Immediately Lead to Human Immortality

However, it's too early to interpret this discovery as "directly leading to human immortality."

The structure of the body and the evolutionary history of sea cucumbers and humans are vastly different. Even if the mechanism by which sea cucumber tissue fragments continue to live in seawater is elucidated, it does not necessarily mean it can be directly applied to human organs, skin, or nerve tissues. Human tissues are more complex and are subject to multi-layered control by blood vessels, immunity, nerves, and hormones.

However, the value of basic research is not determined solely by whether it can be immediately applied. Rather, by discovering phenomena that deviate from the norm, mechanisms that were previously unthought of can become apparent. Why don't the sea cucumber fragments rot? Why can they maintain immune activity? Why can they absorb nutrients from natural seawater? Why can they maintain tissue structure for years?

The answers may include molecules that promote wound healing, mechanisms that delay cellular aging, and hints that enhance tissue infection resistance.

The Unknown Biology Taught by Small Sea Creatures

This research began with an accidental observation. The starting point was when a researcher noticed a small tissue fragment left on the wall of a tank and realized "it's still there." From there, the discussion has expanded to the definition of life, aging, regeneration, medical applications, and ethical research models.

This flow well demonstrates the fascination of marine biology research. The sea is home to countless organisms with survival strategies beyond human imagination. The high-pressure environment of the deep sea, the low temperatures of polar regions, seawater teeming with microorganisms, and the struggle with predators. The mechanisms evolved in such environments are often overlooked in biology based on terrestrial mammals.

The tissue fragments of Psolus fabricii are not from a flashy-looking organism. However, these small fragments overturned the simple assumption of "do tissues that are supposed to die really die?" Life may not only reside in individuals but also persist stubbornly within tissues, in the relationships between cells, and in interactions with the environment.

The fragments of this sea cucumber, called "zombies" on social media, are more of a peculiar messenger demonstrating the flexibility of life than an object of fear. What we call "living" is much broader, more persistent, and still not fully understood than we think.

Source URL

CNN. The main reference source for reports that Psolus fabricii's severed tissues survived for over three years in natural seawater, showing wound healing, nutrient absorption, and cellular activity.
https://edition.cnn.com/2026/05/28/science/sea-cucumber-amputated-tissue-regrowth

Original paper published in Science Advances. The research title is "Natural tissue immortality: Indefinite survival of sea cucumber explants." Primary information reporting the long-term survival of Psolus fabricii tissue fragments.
https://www.science.org/doi/10.1126/sciadv.aeb1394

Expert comments from Science Media Centre Spain. Referencing the significance of the research, potential for regenerative and aging research, and caution regarding the expression "immortality."
https://sciencemediacentre.es/en/tissues-taken-sea-cucumbers-remain-intact-three-years-natural-seawater

Article on Phys.org. Introduction of the research by Bigelow Laboratory for Ocean Sciences, perspectives on marine biology research, and