Like a scarf out of a magician’s sleeve, the squid appeared. Seconds before, there had been nothing.

Isis, a robotic vessel traveling more than 2.5 miles under the Pacific, saw only ocean through its front camera. Another camera, pointing toward the seabed, saw nothing but sediment and some stalks that might have been a dead sea sponge. But a third camera captured a cephalopod swimming away.

Scientists later realized that the unmoving stalks were really the squid. It had been upside down in the mud, with its head and short arms buried, holding its two long tentacles upward in a rigid position. The researchers, who published their discovery last month in the journal Ecology, said the animal might have been mimicking another life-form to avoid predators — or to lure prey. Whatever the squid was doing, the scientists said they were not aware of an earlier observation of a squid behaving so oddly.

The lucky sighting happened while researchers from the National Oceanography Center in Britain were surveying a region of seafloor between Hawaii and Mexico. The habitat here is within what ocean scientists call the abyss — from 9,800 to 19,600 feet deep. No sunlight penetrates. Yet remotely operated vehicles have found diverse life thriving in the dark.

At a depth of about 13,500 feet, the mysterious squid appeared on camera in March 2023. Researchers rewound and scrutinized their footage. “The squid must have come from somewhere,” said Alejandra Mejía-Saenz, a graduate student in deep-sea ecology now at the Scottish Association for Marine Science. Then they realized their cameras had captured the unmoving, branched object becoming the swimming squid.

“We watched the video tons of times until we were convinced,” said Ms. Mejía-Saenz, lead author of the study. “That’s definitely the squid. It’s just behaving very, very strangely.”

They aren’t sure, but the researchers think the animal might be a whiplash squid — which would be fitting, given the double take this specimen caused at the ocean’s surface.

“The way they normally hunt is by taking advantage of how sticky their tentacles are,” Ms. Mejía-Saenz said. Like flypaper, a whiplash squid’s two long tentacles capture tiny crustaceans for the animal to eat.

It’s important for life-forms in the abyss, where food is scarce, to conserve energy. The scientists speculated that their squid might have been posing as one of the deep seafloor’s less threatening creatures, such as a coral, a tube worm or a sponge, to lure prey. Or it could have been disguising itself to hide from deep-diving beaked whales or other predators. Or both.

Other cephalopods are known copycats. In shallow waters, a striped cephalopod called the mimic octopus makes its body into shapes that resemble animals including sea snakes or lionfish. A certain deep-sea squid, when it’s young, has a long tail and positions its body vertically — possibly to mimic a siphonophore, a bizarre ropelike colony of stinging animals.

The hypothesis that the unknown seafloor squid is also mimicking another animal “could be right,” said Mike Vecchione, a retired curator of cephalopods at the U.S. National Museum of Natural History. “But it could also be doing something completely different, and we just don’t know.”

Dr. Vecchione also isn’t convinced that the quickly glimpsed cephalopod is a kind of whiplash squid. He thinks it more likely is a promachoteuthid, a rarely seen type of squid.

That identification is “a plausible alternative,” Ms. Mejía-Saenz said. “Without a physical specimen, we can’t be definitive.”

Whatever the animal’s identity, “it’s doing something that’s very different than other squids do,” Dr. Vecchione said. “It’s a cool observation.”

He said he wasn’t aware of any other reports that a squid had buried itself upside down like this.

The reason scientists were able to make that novel observation, though, is that the squid’s home and weird way of life are being threatened.

In the video from the robotic submersible, Ms. Mejía-Saenz pointed out, there are round stones scattered all over the seabed, a polka-dot backdrop to the squid’s appearing act. They’re polymetallic nodules: rocks high in nickel, copper and cobalt. This region of the Pacific is relatively well studied, she said, because it has been targeted for deep-sea mining. The British researchers’ mission is to gain a better understanding of the seafloor ecosystem and the ways human activities might harm it.

The new observations suggest that many more squid might be hiding in the abyss — and they highlight how much we don’t know about this ecosystem. “Now we’re finding not only new species, but new behaviors as well,” Ms. Mejía-Saenz said.