These Frankenstein-Like Sea Creatures Can Actually Fuse Their Bodies Together

Jellyfish have a myriad of abilities. Some of them are “immortal,” capable of reverting back to their juvenile stage to repeat their life cycle. Others are “brainless,” lacking a nervous system but still able to learn.

Comb jellies, or ctenophores, are transparent creatures that are not closely related to jellyfish, despite their name. But they, too, have a fantastic skill—researchers recently discovered that multiple individuals of a type of comb jelly called the sea walnut can fuse together to become one, sharing bodily functions.

In a study published in Current Biology this month, researchers describe this union, which they suggest happens after an injury. Once fused, the invertebrates can even synchronize their muscle contractions and merge their digestive systems.

“Our findings suggest that ctenophores may lack a system for allorecognition, which is the ability to distinguish between self and others,” says Kei Jokura, a zoologist at the University of Exeter in England and  the National Institutes of Natural Sciences in Japan, in a statement. He adds that these two separate individuals can even join their nervous systems.

Jokura and his team were led to the discovery by trying to recreate a double jelly they’d seen in the Marine Biological Laboratory in Woods Hole, Massachusetts. The odd-looking creature had two heads, two mouths and two anuses. It seemed as though a pair of comb jellies had merged together after sustaining injuries when they were collected.

The team wanted to see if that double jelly had been an outlier. “We did some Frankenstein pilot experiments,” says Mariana Rodriguez-Santiago, a co-author of the paper and a neuroscientist at Colorado State University, to NPR’s Ari Daniel.

In the lab, they cut off parts of sea walnuts’ wing-like features, called lobes, and placed the invertebrates in pairs close together. Nine out of ten times, the jellies would fuse into one—and the mergers survived for at least three weeks.

When Jokura prodded one of these fused ctenophores, all of it twitched in response. That signaled to him the creatures had become one individual and now shared a nervous system. “What was surprising is that this quick response occurred simultaneously in both bodies, even though I had only touched one side,” Jokura says to Science’s Elizabeth Pennisi.

According to the researchers, the merging of the nervous system happened in about two hours. “The extent and the rapidity of that integration is pretty crazy,” says Steven Haddock, a marine biologist at the Monterey Bay Aquarium Research Institute who wasn’t involved in the study, to Scientific American’s Elizabeth Anne Brown.

With further experiments, they found evidence that the digestive systems, too, had integrated. When one of the double jelly’s mouths consumed fluorescent-colored brine shrimp, both anuses eventually ejected waste—but not at the same time.

Comb jelly fusion has been observed before, says Allison Edgar, a biologist at the New Jersey Institute of Technology who wasn’t involved in the study, to NPR, but this is the first time the merged creatures have been documented to behave as one.

Ctenophores are thought to be the first lineage that branched off from the common ancestor of all other animals. Studying them can offer a window into early animal evolution, and this new finding builds on a body of research about basic nervous systems. “Studying how their nervous system works is crucial for understanding the basic principles of neuronal function,” says Oscar Arenas, a co-author of the study and a researcher at the University of California, Berkeley, to the Guardian’s Nicola Davis.

As a result, the discovery could open up new doors to human medicine. “If comb jellies do have this great mechanism for regenerating and healing,” Edgar says to NPR, “that would mean you could have an organ transplant with no consequences and you would heal from it very quickly.”

Jokura partly agrees. Although he isn’t sure how it could improve organ implants in humans, he tells Science, learning how two systems merge “could contribute to the medical research, particularly in nerve regeneration.”

Alexa Robles-Gil | | READ MORE

Alexa Robles-Gil is a bilingual science journalist based in New York City. Her work has appeared in the Guardian, Undark, Inside Climate News and more.