Imagine the thrill of discovering a colossal, elusive monster straight out of an ocean legend, hiding in the shadowy depths off the coast of California – that's the incredible story unfolding in Monterey Bay! This rare encounter not only captivates the imagination but also sheds light on the mysteries of our planet's underwater world. But here's where it gets controversial: is this just a fascinating find, or does it highlight larger debates about how we prioritize exploration in our vast oceans? Stick around, because there's much more to unpack about this seven-armed wonder.
Researchers from California's Central Coast have just made headlines after encountering a massive, hard-to-spot octopus with seven arms during a scientific voyage in Monterey Bay (accessible at https://www.sfgate.com/monterey-carmel/). The extraordinary animal, scientifically known as Haliphron atlanticus, was observed by the biodiversity and biooptics team at the Monterey Bay Aquarium Research Institute on November 6th, as confirmed by the institute in an email exchange with SFGATE. This sighting marks only the fifth time MBARI scientists have laid eyes on this creature over the last 35 years, underscoring just how infrequently it graces our awareness.
To put that rarity into perspective, think of it like spotting a unicorn in the wild – it's not impossible, but it requires a lot of patience and the right tools. The previous encounter happened back in 2017, when researchers learned more about its feeding habits, discovering a preference for jellyfish and other squishy, gelatinous plankton. Fast-forward to last month, and the team, under the leadership of senior scientist Steven Haddock, was investigating the marine ecosystem in the ocean's midwater zone – that's the expansive layer between the surface waves and the dark seafloor, where sunlight fades and strange creatures thrive. At around 2,300 feet deep, they captured footage of Haliphron atlanticus.
Each glimpse of this octopus offers valuable clues about its life in the deep sea, according to MBARI's communications team. For beginners diving into ocean science, the midwater is like a bustling city between worlds: it's not as shallow as the sunlit top where fish dart about, nor as extreme as the crushing pressures of the abyss below. Creatures here adapt to low light and limited food, making every sighting a treasure trove of knowledge.
Haliphron atlanticus roams tropical and temperate waters globally and can grow to an astonishing 13.1 feet long, based on MBARI's data (check out https://www.mbari.org/animal/seven-arm-octopus/). Females of the species can tip the scales at up to 165 pounds, while males are far more petite, typically maxing out at about 8 inches. This size difference is a common evolutionary strategy in many sea animals, where females invest more in reproduction and protection.
The octopus spotted recently was busy devouring a helmet jelly (learn more at https://twilightzone.whoi.edu/explore-the-otz/creature-features/helmet-jellyfish/), a vibrant red, glowing jellyfish that inhabits the ocean's twilight zone. Although jellyfish aren't the most nutrient-packed meal, they're plentiful in these depths, serving as a reliable snack for bigger predators. After munching on the jelly's bell-shaped body, Haliphron atlanticus cleverly repurposes the leftover tentacles as a defensive shield – talk about turning dinner into a survival tool! This adaptation highlights how deep-sea life optimizes every opportunity, a strategy that could inspire human innovation if we paid closer attention.
And this is the part most people miss: despite appearances, Haliphron atlanticus isn't truly short an arm. Like all octopuses, it boasts eight limbs, but one is a specialized appendage for transferring sperm during reproduction. This unique arm stays hidden in a pouch under the animal's right eye, creating the illusion of just seven. It's a fascinating quirk of nature that reminds us how much we still have to learn about evolutionary biology – and here's a controversial twist: some marine biologists debate whether this 'missing' arm makes it less of an octopus, sparking discussions on taxonomy and classification. Is it a true eight-arm creature in disguise, or does this adaptation redefine what we call an octopus? The jury's still out, and it's exactly these gray areas that fuel passionate debates in science.
To capture this elusive giant, Haddock's team relied on advanced remotely operated video equipment, the same technology that recorded the species' first-ever observations according to MBARI. This method allows scientists to explore without disturbing the fragile deep-sea environment, but it also raises questions about the ethics of intrusion: are we justified in peering into these hidden realms, or should we let nature stay undisturbed? It's a thought-provoking dilemma that could divide opinions – do the benefits of discovery outweigh the potential risks?
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Published on Dec 11, 2025
National Parks Reporter
Sam Mauhay-Moore serves as SFGATE's National Parks reporter. Hailing from Long Beach, he pursued studies in journalism and ethnic studies at San Francisco State University. When not enjoying time at home in East Oakland, he's often out truck camping in the mountains or relaxing in hot springs. Reach out to him via email at sam.moore@sfgate.com.
What are your thoughts on this deep-sea discovery? Do you see it as a call to protect our oceans, or perhaps a reminder of how little we know about the planet? And about that taxonomic debate – is Haliphron atlanticus an octopus with a secret, or something entirely different? Share your opinions or any disagreements in the comments below – we'd love to hear from you!
