Scientists accidentally discovered deep-sea ‘jelly’ creatures fused into a ‘single entity’ after an injury

In a fascinating new study, researchers have discovered that comb jellies, or ctenophores, have the unusual ability to fuse together when injured, creating a single entity with a shared nervous system and stomach. This behavior, never observed in any other species, was revealed during routine lab work and offers a new understanding of these deep-sea creatures.

Accidental Discovery in the Lab

The discovery happened unexpectedly during research on warty comb jellies (Mnemiopsis leidyi), also known as sea walnuts, in a lab at the University of Exeter. Researchers noticed that one jelly was missing from a tank, only to realize that a larger jelly was actually two individuals fused together. This accidental fusion occurred when the jellies sustained minor injuries. Excited by the finding, study lead author Kei Jokura immediately shared the discovery with other lab members.

The team then tested whether this fusion could be replicated. They injured 20 comb jellies by removing small sections of their bodies and placed them near each other. Out of the 20, nine pairs fused completely, typically within 24 hours. The merging process also affected their nervous systems, which synchronized rapidly. Researchers observed that the fused individuals reacted as one when poked, indicating a full integration of their neural functions.

Researchers tested how fused comb jellies’ nervous systems worked by poking them on different parts of their conjoined bodies. The pairs’ nerve cells had synced across their bodies after just a few hours of being properly merged. (Image credit: Mariana Rodriguez-Santiago)

Fused Bodies and Stomachs

One of the most surprising aspects of the fusion was that the jellies not only combined their nervous systems but also their stomachs. The team fed the fused jellies fluorescent shrimp to see if their digestive systems had merged. The food was visible moving through both stomachs, confirming that they were functioning as a unified digestive system.

Although these fused jellies acted as a single entity, Jokura clarified that they were not technically a single organism, as they still had separate DNA and could not pass on their fused state to future generations. However, their behavior and function closely resembled that of a single organism, leading the researchers to refer to them as “single entities.”

A Rare Phenomenon in the Wild

This type of fusion has not been observed in any other species, making it a truly unique discovery. The researchers believe that the fusion is likely very rare in the wild, as injured jellies must be in close proximity for the process to occur. Comb jellies are also known for their ability to regenerate lost body parts and reverse aging, so fusing with others may not be a common survival strategy.

Researchers say that injured comb jellies would rarely get close enough to one another to fuse in the wild. (Image credit: Alamy)

The study, published on October 7, 2024, in the journal Current Biology, ended after three weeks, but most of the fused pairs were still alive. Jokura speculated that they could have lived much longer if the study had continued and suggested that more than two individuals could potentially fuse, although this remains untested.

The researchers are now planning to study another comb jelly species, Bolinopsis mikado, to see if they also share this remarkable ability to fuse. This discovery could open up new avenues for understanding the evolution and survival strategies of deep-sea organisms.