On a quiet summer day at the Marine Biological Laboratory in Woods Hole, Massachusetts, Kei Jokura, a Japanese biologist with a fascination for comb jellies, was inspecting his latest batch. As part of his research on how these bioluminescent creatures use light to navigate, he was studying live comb jellies in the lab.
Comb jellies are an ancient animal lineage with a distinct evolutionary history, and despite their similar appearance, they are not closely related to true jellyfish.
Among the golf-ball-sized comb jellies in his tank, he happened to notice one that stood out—a larger, peculiar individual with not one, but two mouths.
As Jokura and his colleague examined the strange creature, they realized it wasn’t a single comb jelly, but two individuals that had somehow merged into one.
What followed was an extraordinary experiment that would reveal a biological adaptation yet unknown to science.
It Takes 2 Hours For 2 ‘Injured’ Comb Jellies To Fuse Seamlessly
After discovering the fused comb jellies, Jokura and his team set out to replicate the phenomenon. Using the comb jelly species Mnemiopsis leidyi—commonly known as sea walnuts—the team carefully designed experiments to understand the mechanics and implications of this fusion.
The researchers began by cutting the lobes—large, soft, and often paddle-shaped appendages—off of two individual comb jellies and placing them in close proximity under controlled conditions.
After two hours had passed, the two were fused without a distinct boundary.
Over the next several hours, the fused individuals synchronized their movements, and food introduced into one’s mouth traveled seamlessly into the other’s digestive system.
This fusion wasn’t just physical—it extended to their nervous systems, allowing the animals to essentially behave as one. The researchers even observed coordinated muscle contractions, further confirming the integration of their biological systems.
To verify their findings, the team repeated the experiment 10 times, varying conditions to ensure robustness. They found that nine out of 10 attempts were successful.
Comb Jellies Can’t Distinguish Between ‘Self’ and ‘Non-Self’
Comb jellies exhibit an unparalleled ability to integrate foreign tissue into their own systems, effectively erasing the boundary between self and non-self.
For most animals, the concept of self versus non-self is vital to survival. However, comb jellies like Mnemiopsis leidyi operate without this biological defense, making them an exception to the rule.
Allorecognition—the ability of an organism to differentiate its own tissues from those of another—is a cornerstone of multicellular life. It underpins immune systems across the animal kingdom, allowing organisms to fend off pathogens, reject foreign tissues and maintain bodily integrity.
The comb jellies’ lack of allorecognition means they do not attack or reject foreign tissue—a feature that played a critical role in the fusion experiments conducted by Kei Jokura and his team.
Comb Jellies Adapt An Alternative Means Of Survival
The absence of allorecognition in comb jellies raises profound questions about the evolution of multicellular life.
If these ancient creatures can thrive without immune systems that distinguish self from non-self, it could challenge long-held assumptions about the necessity of such systems for survival. This could mean that allorecognition evolved not as an essential feature of multicellularity but as a specific adaptation to certain environmental pressures or biological threats.
Moreover, the comb jelly’s lack of allorecognition opens up exciting possibilities for scientific exploration. Understanding how their cells integrate foreign tissue without rejection could lead to breakthroughs in regenerative medicine and transplantation.
Comb jellies stand out even in a sea teeming with unique creatures. Does their fascinating adaptation inspire you to seek a deeper bond with the natural world? Take a 2-minute test to know where you stand on the Connectedness to Nature Scale.
