Rare Footage Reveals the Mysterious Seven-Arm Octopus Eating Its Prey

Lurking in the ocean’s twilight zone — an area between 650 and 3,000 feet below the surface where light rarely reaches — is the seven-arm octopus (Haliphron atlanticus). Also known as the septopus, giant gelatinous octopus, or blob octopus, this massive cephalopod is one of the largest octopuses on Earth, with the heaviest specimen recorded weighing in at 165 pounds, according to the BBC.

Now, researchers at the Monterey Bay Aquarium Research Institute (MBARI) have recorded footage of this deep-sea dweller.

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Rare Footage of the Seven-Arm Octopus

The new video shows the octopus feeding on a red helmet jellyfish. The burnt orange octopus’s legs are tucked into its body, giving it the appearance of a floating lozenge, with one dark eye winking from its side. The footage shows the octopus eventually wrapping its arms around the jellyfish as it drifts through the ocean. The jellyfish later disappears entirely from view as the octopus finishes off its meal.

The research team at MBARI has recorded footage of only a few seven-arm octopi over several decades of oceanographic study, although specimens have been recorded very sporadically by other teams. The last time they filmed a specimen, in 2017, it was also clutching a jellyfish, although on this occasion it was an egg-yolk jelly.

Seven-Arm Octopus Diet

Subsequent analysis of museum specimens confirmed that jellyfish make up a substantial proportion of these octopuses’ diet, which was surprising to the researchers, given that such jellyfish are mostly made of water and are virtually calorie-free, according to a report from the University of Southern Denmark.

The octopuses eat the tissues in the jellyfish’s body, or bell, and then pull the prey’s stinging tentacles along behind them, potentially as a type of defense against predators. Other evidence has shown that they also feed on less gelatinous prey, such as shrimp, according to a report from the University of Gothenburg.

"To be able to confirm our first observation with this new sighting was informative because this octopus was holding a different, deeper-living type of jellyfish than we'd seen before," said Steven Haddock, a marine biologist at MBARI and part of the team that filmed the octopus, in an interview with the Los Angeles Times. The images were recorded by a remotely operated vehicle operating at a depth of approximately 2,300 feet.

"It was super exciting for me to see this species that I had only seen once before," Haddock said. "It is also interesting that this octopus is one of the largest known species, yet it reaches these sizes (on) a gelatinous diet."

This Octopus Hides Its Eighth Arm

The “seven-armed” octopus actually has eight arms. Males of the species tuck away their eighth arm into a specialized pouch located beneath their right eye. This gives the appearance of the animals missing one of their arms.

This eighth arm is a specialized structure called a hectocotylus arm, which lacks suckers at its tip and is adapted for sperm transfer during mating. This arm also lacks chromatophores, which enable the rest of the octopus to change color. This means the eighth arm would make a camouflaged octopus obvious to prey or predators, which is why they have evolved to tuck it away.

Female seven-arm octopuses are larger than their male counterparts, growing up to 13 feet long. The males, in comparison, are less than a foot long. Perhaps unsurprisingly, after tussling with this extreme sexual dimorphism, males die after mating. Females often die after laying eggs or releasing their young into the ocean.

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Article Sources

Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:

• This article references information from the BBC: Giant octopus puzzles scientists
• This article references information from the University of Southern Denmark: Jellyfish contain no calories, but they still attract predators
• This article references information from the University of Gothenburg: Unusual catch of octopus benefits science
• This article references information from the Los Angeles Times: Rare, deep-sea encounter: California scientists observe ‘extraordinary’ seven-arm octopus