A little more than a year ago, while biologist Kei Jokura was in Woods Hole, Mass., he routinely walked down to the water, scanning for comb jellies.
"They look like a jellyfish," he says, "but they're completely different." It's a blob the size of a silver dollar with little hairs that ripple along the edges of its mostly see-through body. Jokura says it's possible that the first nervous system to ever evolve on Earth was inside an ancient comb jelly — a distant ancestor of the ones he was scooping out of the water.
He likens the search to a thrilling kind of treasure hunt. "You can definitely miss it," he says, but his trick is to look for sunlight reflecting off of their bodies.
Jokura took the comb jellies he found back to the lab in Woods Hole and put them in a tank. One day, he went to check on them and a particular comb jelly caught his eye — one that led to a paper just published in the journal Current Biology.
"I was surprised because a weird shape was there," he recalls. It was fatter. It had two heads, two mouths, and two anuses. Jokura thought to himself: "Oh, I think these are two individuals fused together."
He took off at a sprint, fat comb jelly in a beaker, to show his labmates. "I was like, 'What? That's weird," says neurobiologist Mariana Rodriguez-Santiago of Colorado State University. "And so I went to see it and I was like, 'Oh, it is fused. Oh, and it's moving together.'"
This was a striking observation — if this being was once two individuals, it was now behaving as one.
The next thing Rodriguez-Santiago did was to poke it. "I poked it mostly to see if they would get unstuck," she says. "But instead, the muscle contracted at the same time." This suggested that it had a shared nervous system.
The researchers went about trying to see if this little translucent fatty was an anomaly or whether they could recreate it. "So we did some Frankenstein pilot experiments," says Rodriguez-Santiago.
They sliced comb jellies in different spots, and when they snipped them along their edges and placed them near one another, within an hour or two, they fused nine out of ten times.
In addition, the team fed the fused jellies brine shrimp with fluorescent dye so they could keep track of the food particles. "One comb jelly ate it and it traveled through the gut of both of them and the second comb jelly pooped it out," says Rodriguez-Santiago.
"I thought this was a really fun paper to read," says Allison Edgar, an integrative biologist at the New Jersey Institute of Technology who wasn't involved in the research. She says comb jelly fusion has been observed before, but this is the first time that scientists have documented the individuals behaving as one.
Edgar is excited by what this discovery might mean for humans. "If comb jellies do have this great mechanism for regenerating and healing," she says, "that would mean you could have an organ transplant with no consequences and you would heal from it very quickly."
She says given how rapidly the two comb jellies' nervous systems became one, it could teach humans how to allow someone to regain full control over a transplanted limb, say. But she admits that kind of advance is a ways off.
In other words, comb jellies may be transparent — but they hold secrets that are still very much opaque.
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