'Very novel and very puzzling': Unknown species of squid spotted burying itself upside down, pretending to be a plant

Scientists have filmed a never-before-seen species of deep-sea squid burying itself upside down in the seafloor — a behavior never documented in cephalopods. They captured the bizarre scene while studying the depths of the Clarion-Clipperton Zone (CCZ), an abyssal plain in the Pacific Ocean targeted for deep-sea mining.

The team described the encounter in a study published Nov. 25 in the journal Ecology, writing that the animal appears to be an undescribed species of whiplash squid. At a depth of roughly 13,450 feet (4,100 meters), the squid had buried almost its entire body in sediment and was hanging upside down, with its siphon and two long tentacles held rigid above the seafloor.

"The fact that this is a squid and it's covering itself in mud — it's novel for squid and the fact that it is upside down," lead author Alejandra Mejía-Saenz, a deep-sea ecologist at the Scottish Association for Marine Science, told Live Science. "We had never seen anything like that in any cephalopods. … It was very novel and very puzzling."

Mud covering and burial have been seen in octopuses and cuttlefish, and even in shallower-water squid species before. However, these behaviors had never been documented in a deep-sea squid before — and never upside down.

"It was so exciting and unexpected to observe burying behaviour in a deep-sea squid, something that has never been seen before!" study co-author Bethany Fleming, a researcher at the University of Southampton and the National Oceanography Centre in the U.K., said in a statement emailed to Live Science.

Masquerade on the seafloor

The encounter happened during the SMARTEX project, a U.K.-led expedition to study how deep-sea mining might affect life in the CCZ. The team's remotely operated vehicle (ROV) was filming across a commercial exploration area, when the squid appeared underneath it, with its tentacles looking like the stalks of glass sponges or large tube worms that dot the seemingly barren abyssal plain.

At first the squid underneath the ROV, seemingly unaware of its existence. It was then that the researchers realized it was a type of squid due to its movements and body traits. However, the squid then seemed to disappear from camera.

“[Fleming] first saw this and said ‘wait a minute, is the squid actually there?’ Because the only thing we could see were two white things sticking out.” Mejía-Saenz said.

The case of the disappearing squid was quickly solved when the researchers realized it had buried itself. From watching the squid, the team believes it is camouflaging itself, proposing potentially two reasons why it had buried itself with its tentacles poking out: it was trying avoid predators like beaked whales or it had seen crustaceans, its favorite prey, crawling around the glass sponges in the area and was mimicking the sponges with its tentacles to attract a snack. "We thought, 'okay then if the sponge is attracting the crustacean and the squid is imitating the sponge and it eats the crustacean, that would make sense'," Mejía-Saenz said.

If that's right, the squid may be using a strategy biologists call masquerade — looking like an inedible object so predators ignore it — combined with a booby-trap for prey. In the food-poor abyss, that kind of ambush could be a smart energy trade-off, as animals waste less energy waiting for food to come to them than they would chasing it, all while remaining invisible to nearby threats.

Jim Barry, a senior scientist at the Monterey Bay Aquarium Research Institute (MBARI) in California who was not involved in the study, agreed that the squid appears to be mimicking the glass sponges seen in the CCZ. "When the squid assumes the charade behavior it is similar to some seafloor invertebrates (sponges, soft corals, polychaete worms) that inhabit the region," he told Live Science in an email.

Why abyssal squid are so rarely seen

Deep plains like the CCZ cover vast areas of seafloor, yet they remain among the least-explored habitats on the planet. "The ocean is huge," Mejía-Saenz said, and abyssal plains "are one of the least explored parts of the ocean."

Even in this comparatively well-studied zone, the team's broader survey found just 33 cephalopod encounters across roughly 3,100 miles (5,000 kilometers) of ROV tracks. That tiny tally helps explain why behaviors like mud-covering masquerade are only now coming to light.

"Considering the very limited observations that have been made at abyssal depths, it may not be surprising to discover a new species," Barry said. "Abyssal squids are very rare and those with a mimicking behavior are even less known to science. …the main reason we know so little about deep sea cephalopods is [the] very limited amount of effort that has gone into exploring the deep-sea."

Mining into the unknown

What makes this single squid especially worrying is where it was seen. The CCZ is the primary target for the proposed deep-sea mining of nickel, cobalt, manganese and other metals used in batteries.

"The reason why we know so much about the CCZ is because there are commercial interests on it," Mejía-Saenz said. To retrieve the valuable minerals, mining vehicles would stir up sediment plumes that blanket nearby life. "Disturbance to the seafloor would have negative consequences mostly likely for these animals," she said. "The extent of those consequences, we still don't know."

Barry said we increasingly depend on deep-sea resources. In potential mining zones, "there is much at stake," he said, "and it is imperative that we understand at a minimum what life inhabits these sites and how vulnerable these biological communities are to human activities."

Bruce Robison, an MBARI scientist who was not involved in the study, said discoveries like this mud-covered squid highlight the limits of our knowledge.

"Deep-sea squid are fast, agile, and wary, so they only let us see them when they want to, or when they just don't care," he told Live Science in an email. "We must have observed only a very small fraction of their behaviors. It's always surprising to learn about a new (to us) tactic that squids have in their bag of tricks."