Comb Jellies Have Frankenstein-Like Ability to Fuse Together When Injured

When injured, pairs of comb jellies can seamlessly fuse together to become one fully functioning entity – like Frankenstein’s monster in reality.

Researchers in the UK accidentally stumbled across this freaky ability when they found a two-butted, oddly large individual among their group of captive sea walnuts (Mnemiopsis leidyi).

Upon poking what used to be a solitary half of the now fused individuals, the whole conjoined creature flinched in response, suggesting that the once-separate nervous systems are now fully integrated with each other, as captured in a video.

“I was surprised when the muscle contractions of the fused comb jellies became synchronized,” explained University of Exeter bioscientist Kei Jokura.

Not only did their nervous systems meld, but their digestive systems fused as well.

“The fused comb jellies have two mouths,” Jokura explained. “When food was given to one side, the digested material was transported to the neighboring digestive tract.”

Interestingly, the resulting waste was expelled from both of their retained butts at different times.

Previous studies have found that sea walnuts, a species of comb jellies, have rapid regenerative abilities, making them a popular laboratory model for wound healing. Jokura and a team of international researchers tested a hunch to replicate their bizarre discovery.

They injured a number of sea walnuts, taking a slice along each one’s side lobes and keeping them isolated in pairs overnight. The next day, they found that nine out of ten pairs of M. leidyi had fused seamlessly into a single body.

Observations showed that initially, each member of the merged jellies moved independently, but within two hours of their fusion, the majority of their muscle contractions were synchronized, indicating full integration of their nerve nets – comb jelly’s simple nervous systems.

The researchers have yet to confirm if sea walnuts can also perform this astonishing fusion in the wild. This species of Ctenophore floats freely among planktonic life on the ocean’s surface, making it unlikely for them to encounter a potential fusion partner frequently.

However, Jokura and the team speculate that the ability to fuse may provide an evolutionary advantage, allowing for faster recovery from injury compared to regeneration. The biological fusions still appeared perfectly healthy three weeks after their merger.

Despite their name and gelatinous forms, comb jellies – known for their dazzling, rainbow-refracting, hair-like tentacles – are only distantly related to true jellyfish. These predators can be found from the surface to the depths of the ocean and range in size from a few millimeters to around 1.5 meters.

Ctenophores are part of such an ancient lineage of animals that their ancestors are leading contenders for the first multicellular animal to have ever existed on Earth.

The ability of individual jellies to fuse so completely with each other suggests they lack the mechanisms most other animals have for recognizing ‘self’ from ‘non-self’. This allorecognition is what makes blood and organ donations challenging between humans.

Jokura is eager to investigate the mechanisms behind how the two individual animals’ neural activity combines so effectively.

“The allorecognition mechanisms are related to the immune system, and the fusion of nervous systems is closely linked to research on regeneration,” Jokura said in a press release. “Unraveling the molecular mechanisms underlying this fusion could advance crucial research areas.”

This research was published in Current Biology.