Immortal Jellyfish

7 Sept

Turritopsis dohrnii

The immortal jellyfish is so-called because it can revert to a previous stage in its life cycle due to stress or injury. However, this isn't immortality as we typically think of it: the jelly turns back into a stationary polyp that spawns several genetically identical medusae.

For all recorded history, the idea of immortality has been a fascination, a desire, and, to some, an obsession.

One of the earliest surviving epics, The Epic of Gilgamesh, was about a Sumerian king seeking an escape from death after the loss of his friend. Pantheons of immortal gods ruled over mortal humans. The Hindu devas drank a nectar of immortality from the cosmic ocean. The gods of Greece and Scandinavia had magical apples that granted eternal life, while in Chinese myth, peaches were the fruit of everlasting youth.

The first emperor of China sought immortality so zealously that it led to his premature death at the age of 49, after consuming concoctions of mercury (he would've been better off eating peaches). Alchemists, too, sought nothing less than great wealth and eternal life, distilling their dreams into the philosopher’s stone, said to transmute base metals into gold and produce the Elixir of Life.

The idea of life-giving waters, a Fountain of Youth, has meandered its way through history like a river of thought, moving through time — from Herodotus, to Alexander the Great, Prester John, and the Age of Exploration — and space — beyond the bounds of the known world, just off the charted portions of the map, always out of reach.

We did eventually find immortality, and we did find it in the water. Just not in the form we expected.

The Immortal Jellyfish

In 1883, a new species of jellyfish was discovered off the coast of Italy, described and christened Turritopsis dohrnii. It seemed a pretty unremarkable animal.

Just like any jellyfish, T. dohrnii begins life as a larva developed from an egg. After a bit of swimming about, it settles on the sea floor and becomes a sessile colony of polyps. Finally, this colony releases into the water column many genetically identical medusae — the free-swimming forms most people imagine when thinking of jellyfish.

In its medusa form, T. dohrnii has a transparent bell-like body, its red stomach visible inside, surrounded by around 90 wispy tentacles. With a diameter of just 4.5 millimetres (0.18 inches), it could fit easily on a fingertip. No one thought to look for immortality in a minuscule jellyfish.

It was only in the 1980s, a hundred years later, that its mythical ability was discovered. Collected from the eastern Italian Riviera, several of these jellyfish were kept in a jar and monitored. One day, when the researchers returned to check on their jelly jar, they were surprised to see new polyps settled at the bottom — surprised because their jellyfish had not yet matured. These polyps couldn’t have come from spawned larvae.

Observing the jellyfish more closely, they found that T. dohrnii medusae would drop to the glass bottom and — bypassing fertilisation, spawning, and the larval stage altogether — would simply transform back into polyps. Over time, these polyps would produce new clonal medusae, each with a bright red stomach, like tiny vessels carrying fragments of the Philosopher’s Stone.

T. dohrnii would come to be known as the immortal jellyfish.

The Instruments of Immortality

The life cycle of a typical jellyfish (hydrozoan) vs. the immortal jellyfish.

The immortal jellyfish does what alchemists never could.

The transmutation of baser metals, such as iron or lead, into gold was never achieved. Neither did they find their life-giving elixir.

The jellyfish has a power that could be described as biological transmutation — technically known as transdifferentiation. It can transform its adult cells, which are already specialised for a particular tissue, into a different type of cell; repurposing muscle, nerve, or digestive cells into entirely different tissues.

That's how the immortal jelly reverts back into a polyp.

A jellyfish polyp and medusa are made up of different cell types, and, in most jellyfish, once they mature into a medusa, their cells no longer change. The immortal jellyfish can play this process in reverse. Through transdifferentiation, it transforms its mature medusa cells back into the cells of a polyp, forming a completely different body plan, effectively rewinding its life cycle.

Unconventional Immortality

If ancient, immortality-obsessed emperors had known about these jellyfish, they would surely order them ground down into elixirs, hoping to absorb some of their essence. But what would that entail?

The different life stages of the immortal jellyfish by William K. Brooks, 1910.

For one, the immortal jellyfish isn't truly immortal. Through its ability to transdifferentiate its cells, it can cease the march of senescence — halting the deterioration that comes with ageing — and repair some damage taken to its body by reverting to the polyp stage. But while it may be immune to the effects of time, it can very much still die. Predation, disease, or a change in environment can cut short its potentially endless existence.

Furthermore, the ability of T. dohrnii, while extraordinary, isn't quite the immortality we've so long dreamed about. It's more of a chance to begin anew. If a human equivalent can be made, it would be like reverting to a fetus whenever you became too old, injured, or stressed. But even that doesn't quite capture the strangeness of the immortal jellyfish.

Since the reverted polyp goes on to produce multiple, genetically identical medusae, it's more of an eternal cloning operation than a single, immortal life. The whole process is difficult to overlay onto human biology, given how different our life histories are compared to the multi-stage lives of jellyfish. If a human had the immortality of the immortal jellyfish, it might be more alien body horror than godhood — your current body dissolving into an immobile mass that churns out adult clones of yourself.

The Eternal Search for Everlasting Life

We've never quite stopped our search for the golden apple, the philosopher's stone, or the Fountain of Youth. But rather than exploring distant lands through spyglasses or gathering ingredients for the Great Work, we now peer down microscopes and decode genomes. Beneath the bizarre biology of the immortal jellyfish lies the potential for insights into ageing, regeneration, and disease resistance.

The secret won't be as simple as taking DNA from an immortal jellyfish and splicing it into the human genome. For one, the immortal jellyfish doesn't have an "immortal gene," although its genome is quite extraordinary. A study comparing its genome to a close relative — the crimson jelly (Turritopsis rubra) — found that the immortal jelly has double the amount of genes for repairing and protecting DNA; genes that may produce a greater amount of restorative proteins, which detect DNA damage and recruit repair enzymes. Could a similar duplication be made in us to a positive effect?

Then there's the subject of telomeres. These are protective caps of repetitive DNA sequences located at the ends of chromosomes that become shorter and shorter over an organism's lifetime, as cells continuously divide. This shortening is considered a major factor in cellular ageing and is linked to the development of age-based diseases. And the immortal jellyfish? During its unique rejuvenation process, it shows reduced expression of genes linked to cell proliferation and increased expression of those involved in telomere protection — such as the telomerase reverse transcriptase gene (TERT). In other words, these features suggest that T. dohrnii may limit unnecessary cell division and slow the shortening of its telomere, potentially slowing cellular ageing.¹

If the length of telomeres truly is such a big factor in biological senescence — and many studies do treat short telomeres as a driver of ageing that can impact multiple pathways (DNA damage, inflammation, etc.) — could the immortal jellyfish teach us how to engineer our cells to divide more "deliberately," conserving telomere length, and so keep cells in a youthful state for longer? Maybe. More research is needed.

Finally, there's the jellyfish's cellular superpower: transdifferentiation. In most organisms, once a cell has become specialised — into a skin cell, lung cell, brain cell, etcetera — it remains that type of cell. But, as we've seen, the immortal jellyfish can directly convert mature cells into different types. This contrasts with humans, where cell regeneration typically relies on special, undifferentiated cells, known as stem cells, capable of becoming many cell types. Understanding how the jellyfish’s cells bypass the stem cell stage to reprogram themselves could revolutionise regenerative medicine, offering new ways to promote tissue repair and combat ageing by activating or imitating stem cell-like plasticity in human cells.

This, no doubt, is a very different kind of immortality. There are no golden apples or elixirs. There is research into complex, multi-layered mechanisms, into genomes and cells, looking for tricks that, in jellyfish, rewind the clock and restart a life cycle, in hopes of discovering some way to apply that to our own, very different biology.

Our best hope for, if not immortality, then increased health and longevity, lies in the river of shared descent. It is because organisms share a common ancestor, and so the same base instructions, that the secrets of one organism — as different as a jellyfish and a human — can be shared.

The dream of conquering death lives on. The long path has led us from fountains of youth and philosopher's stones, to an uncertain promise in the form of a tiny "immortal" jellyfish.

¹ No direct evidence has yet confirmed that telomere length is maintained indefinitely, nor have specific mutations in the immortal jellyfish's genome been identified that completely prevent telomere deterioration. The relationship between its unique expression of genes (pertaining to cell division) and the prevention of telomere deterioration is inferred from correlations, though consistent with broader findings that link the preservation of telomere length to longevity.

**Where Does It Live?**

⛰️ Temperate and tropical waters.
📍 Worldwide.

Size // Tiny
Length // 4.5 mm (0.18 in)
Weight // N/A
Activity: N/A
Lifestyle: N/A
Lifespan: Theoretically infinite
Diet: Carnivore
Favorite Food: Planktonic creatures and tiny fish eggs ⋆｡˚
Phylum: Cnidaria
Class: Hydrozoa
Order: Anthoathecata
Family: Oceaniidae
Genus: Turritopsis
Species: T. dohrnii

Turritopsis dohrnii, a jellyfish just 4.5 millimetres (0.18 in) in diameter,is known as the immortal jellyfish because it can, theoretically, live forever — although its version of immortality is an odd one.
A typical jellyfish goes through several life stages. It begins life as a larva developed from an egg. After a bit of swimming about, it settles on the sea floor and becomes a sessile colony of polyps. Finally, this colony releases into the water column many genetically identical medusae — the free-swimming forms most people imagine when thinking of jellyfish.
What makes T. dohrnii special is its ability to move backwards through this cycle: upon encountering stress or injury, it transforms back into its grounded polyp stage. From there, it spawns a new set of genetically identical medusae. But while it could theoretically live forever, in this way, it could also perish from predation, disease, or a change in environment.
It accomplishes this reversal through a process known as transdifferentiation, wherein it transforms its adult cells, which are already specialised for a particular tissue, into a different type of cell; repurposing muscle, nerve, or digestive cells into entirely different tissues.
It's not the kind of immortality that's easily transferable to humans. It would be like your body dissolving into an immobile mass that churns out adult clones of yourself.