Untangling The Long-Armed Mystery Of The Bigfin Squid

The elbowed, spindly appendages of the bigfin squid have long stunned the public. But scientists say there is more to this deep-sea dweller than its ghostly appearance.

a deep sea squid with a pinkish white body and very large fins gentle waving. beneath its body are extremely long, thin arms and tentacles held in a bent position before they drift below into the deep dark sea
A long-armed “mystery squid” observed by MBARI’s ROV Tiburon off the coast of Oahu at a depth of 3,380 meters in May 2001. This individual was estimated to be four to five meters long. It was one of the eight videos cephalopod curator Mike Vecchione came across in trying to identify the creature. Credit: © 2001 MBARI

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Archive Entry: December 21, 2001

Cephalopod Week logoAs curator of cephalopods at Smithsonian National Museum of Natural History, Mike Vecchione is no stranger to the occasional inquiry about unknown creatures dwelling in the deep sea. But in 2001, he received a call that immediately grabbed his attention.

A woman in Louisiana described an odd, large squid—more than 20 feet long—that her boyfriend had filmed while remotely operating an oil company vehicle in the Gulf of Mexico. He thought, “That’s got to be a giant squid,” an elusive species that biologists had been trying to capture alive on camera for decades.  

an eerie old video tape from a deep sea submersible of a strange squid suspending vertically by its large fins. as the camera and lights of the sub pan down, you see its long tentacles and arms extend down into the darkness
The first video Vecchione received, filmed in January of 2000, unveiled an unusual squid with a craned arm posture when it was first encountered in the Gulf of Mexico. Credit: Michael Vecchione et al, Science, December 21, 2001

But the grainy footage was not of a giant squid. In fact, it was unlike anything Vecchione had ever seen or heard of before: A squid suspended by undulating fins much larger than its body, with long, spindly arms bent sharply before draping down into the darkness like ghostly gossamer.

“My reaction was to jump out of my chair and start yelling profanities, because I knew it was something really different,” Vecchione remembers in a recent phone interview with Science Friday.

He reached out to fellow cephalopod researchers and squid biologists, but like Vecchione, no one knew what it could be. Vecchione was able to track down eight more sightings from deep-sea submarines around the world that hadn’t been documented or shared with researchers. He and his colleagues published the findings on December 21, 2001 in Science. That same day, he spoke to Science Friday about the obscure animal that he and scientists had dubbed, “the mystery squid.” 

In the two decades since, the “mystery squid” has been identified and given a scientific name, Magnapinna, better known as the bigfin squid. But its elbowed, slender arms and unearthly visage have also attracted other nicknames, like the “long-arm squid” and “daddy long legs of the ocean,” and recently “ghost of the sea,” as described by squid biologist Sarah McAnulty.

a zoomed out camera view of a squid showing its long extensions before zooming in closer to see its flapping fins
Credit: Michael Vecchione et al, Science, December 21, 2001
a close up shot of a squid with large undulating fins and a better look at the sharp elbow bends in the tentacles and arms
Credit: Michael Vecchione et al, Science, December 21, 2001

Another bigfin squid spotted by the Alvin submarine in the Gulf of Mexico, October 2000. Credit: Michael Vecchione et al, Science, December 21, 2001

While more recordings have surfaced over the years, these phantoms of the deep are still a rare sight. They live at extreme depths of nearly 4,800 meters. This year, a research sub diving to the USS Johnston, a sunken World War II naval destroyer in the Pacific Ocean, stumbled across a bigfin squid in the deep trenches of the hadal zone. It was swimming at a little over 6,000 meters, making it the deepest squid ever recorded, Vecchione tells SciFri

Increased interest and advancements in deep-sea technology have allowed researchers to discover more about the bigfin squid—like the potential purpose of those lanky arms and tentacles, an estimate of the species’ range, and where they fit within the evolutionary tree of cephalopods. 

a white colored juvenile squid with very large heart shaped fins, larger than its body. it has short stubby looking tentacles
A juvenile of the type species M. pacifica. Credit: Richard Young and Michael Vecchione, South African Journal of Marine Science, 1998

Back in 1991, Richard E. Young, professor emeritus at the University of Hawaii and one of Vecchione’s frequent collaborators, described several peculiar squid paralarvae that had been caught in waters around the Hawaiian islands. He called the new family of squids “bigfin,” after their very large, heart-shaped fins. But Vecchione and Young, who had seen baby and juvenile specimens of these unknown squid, had never spotted one alive or in their adult stage—until 2001.   

“We suspected that this new squid that we had gotten the video of might be the grown up of those, but we didn’t know for sure,” Vecchione says. It wasn’t until 2006 that a key specimen in a later developmental stage, collected by marine scientist Tracey Sutton, revealed structures growing at the tips of the short, stubby arms and tentacles—the beginnings of the long, thin extensions seen on the “mystery squid.” “That allowed us to make the connection,” he says. 

Researchers have since been able to identify several species of Magnapinna, and DNA analysis on tissue samples have also shed some light on their evolutionary history. They are related to another group of deep-sea cephalopods called Mastigoteuthis, which have two long sticky tentacles. 

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A bigfin squid spotted in the Gulf of Mexico by NOAA Okeanos Explorer Program during a 2012 expedition. Initially, one of the scientists thinks it’s a jellyfish. Credit: NOAA Okeanos Explorer Program

Like other squid, bigfin squid have eight arms and two tentacles—each covered with microscopic, sticky suckers. But the arms and tentacles are indistinguishable from each other, which “is really unusual for a squid,” says Vecchione. He explains that other squids use their tentacles very differently than they use their arms. “For the bigfins, because they’re really not modified, we assume that they use the tentacles the same way that they use the arms,” he explains. Vecchione suspects that as the squid flutters up, the sticky “spaghetti-like” extensions cast downward like a long net, waiting for small crustaceans or other planktonic prey to bump into them.

“Basically, they’re a living spider web.”

In addition to their length, bigfin squid appendages bend oddly, sort of like dangling puppet strings. A team of marine scientists, led by Australia’s national science agency, CSIRO, were conducting a remotely operated vehicle (ROV) to survey deep-sea habitats in the Great Australian Bight when they got an unexpected look at the bigfin squid and its legendary “elbow pose.”  

“I was sitting in the video lab alone, but I think I let out a little yelp of excitement before sharing with my colleagues what I believed we had captured on film,” says Deborah Osterhage, a University of Tasmania graduate student who was on the team. 

A bigfin squid gets caught in a vortex generated by the ROV’s thruster turbulence. The video was taken by ROV on March 25, 2017 at a depth of approximately 3,056 meters. Credit: Osterhage et al, PLOS One, November 11, 2020

The expedition’s observations of the bigfin squid published in PLOS ONE in 2020. In newly recorded footage, the turbulence from the ROV thrusters sent the squid spinning, its dainty arms and tentacles swirling behind—suggesting that the filaments have little muscle, and likely rely on water movement to maintain their characteristic pose, Osterhage explains. “By extending their arms in this way, it may help avoid getting their ‘fishing lines’ tangled,” she says.

The team also spotted a surprising behavior never before seen in squid: its filaments coiled up, “a little like an old-school telephone cord,” says Osterhage. “We are unsure what this represents, but the filaments are believed to be retractable, and such coiling may represent the means of retraction.” These sightings were the first time the bigfin squid had been seen in Australian waters. The observations supply more evidence that it’s widely distributed in deep water habitats around the world, Osterhage says.

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two photos side by side of squid showing extremely long thread like arms and tentacles
ROV images of a Magnapinna squid at a depth of 3,060 meters in the Great Australian Bight. Credit: Osterhage et al, PLOS One, November 11, 2020

The team didn’t just observe one bigfin squid, but had five individual sightings. Though past observations have been mainly of one squid, the researchers found these ones clustered in close proximity to each other, both in time and space, despite their surveys covering a large area. This clustering is often associated with specific environmental needs or increased reproductive opportunities, Osterhage says. 

Vecchione, who reviewed and confirmed the identity of the squid in the 2020 study, also noted that the number of sightings in close range was “remarkable.” He suggests that patterns of deep currents in the Great Australian Bight could be another potential reason for causing deep drifting animals, like bigfin squid, to aggregate, similar to how trash concentrates in the gyre of the Great Pacific Garbage Patch.

“It seems otherworldly.”

“Bigfin squid have only been filmed around a dozen times around the world over the past 30 years, so seeing five in the Great Australian Bight has been very exciting,” Osterhage says. Deep-sea expeditions have increased since 2001, Vecchione says, but the extreme pressure and cold temperatures still make it challenging to explore and require expensive, specialized equipment. The expedition “has given us a real peek into the deep, dark world of these squid.” But she adds that much of this vast deep ocean remains unexplored. 

We know little about its diverse environments or the various lifestyles of animals that live there. Yet under a warming, rapidly-changing planet, learning about these ocean creatures is essential. “With increasing pressures on the deep-sea environment,” Osterhage says, “it is important to get baseline data to understand how such pressures may impact the deep sea and its residents, such as the bigfin squid.” 

The bigfin squid is symbolic of many of the ocean’s extremes and mysteries. Yet undisturbed, it carries out an ethereal existence—daintily drifting in the inky abyss: “It seems otherworldly,” Osterhage says. “Although some people find them a bit spooky, I find their coloration delicate, and their flapping fins and trailing arms and tentacles quite calming.”

A bigfin squid swimming serenely. Filmed by ROV on March 24, 2017 at a depth of approximately 3,060 meters. Credit: Osterhage et al, PLOS One, November 11, 2020

Archival interview excerpts have been edited for length. 

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Lauren J. Young was Science Friday’s digital producer. When she’s not shelving books as a library assistant, she’s adding to her impressive Pez dispenser collection.

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