Exotic spotlight
Giant Antarctic Octopus: the world's largest octopus lives under the Southern Ocean ice
The Giant Antarctic Octopus (Megaleledone setebos) is the heaviest octopus in the world, a smooth-skinned, pale-bodied predator living beneath Antarctic ice at depths of up to 2,200 m. It is one of the least-observed animals on Earth, with fewer than four confirmed sightings on record worldwide.
Most octopuses live where divers can find them: on coral reefs, rocky coasts, in tide pools. The Giant Antarctic Octopus has chosen a different neighbourhood. It spends its life beneath the Antarctic ice shelf, in water close to the freezing point, in almost total darkness, at depths that would crush an unprotected human body flat. We know it exists. We barely know anything else.
What it looks like
Unlike most octopuses, Megaleledone setebos has smooth skin rather than a bumpy or warty surface. Its colouring is pale reddish-brown, sometimes almost translucent in cold water. The arms are connected by unusually wide webbing, making the animal look more like a broad-skirted umbrella when it spreads. The mantle (the head-body section) reaches up to 32 cm across in large adults.
It belongs to a monotypic family, Megaleledonidae: the only species in its genus, and the only genus in its family. This is not a variant of a common octopus. It is a lineage all its own.
Where it lives and why you will almost certainly never see one
The Giant Antarctic Octopus is circumpolar: it has been recorded around the entire Antarctic continent, wherever the Southern Ocean's seafloor offers rocky substrate and cold, near-freezing water. It prefers depths of 100 to 2,200 m, which puts much of its range well below any recreational or scientific dive.
Access to its habitat requires research submersibles, remotely operated vehicles, or trawl nets from icebreaker ships. Even then, sightings are almost vanishingly rare. Fewer than four individuals have ever been reported to iNaturalist, making this one of the least-observed animals in the entire Kaught catalog. The Legendary tier reflects exactly that: not a quality judgement, but a hard count of confirmed wild encounters.
What it eats, and its venom
In near-total darkness at the seafloor, M. setebos hunts fish, crustaceans and other cephalopods. Like all octopuses, it uses venom delivered through its beak to immobilise prey. The venom acts quickly at low temperatures, which is important in cold water where metabolism slows and a prolonged struggle would waste energy. Once subdued, the beak bites through shell or skull to reach the tissue inside.
Its wide arm webbing helps it engulf prey before the arms fully close, a technique seen in several deep-sea octopuses that ambush mobile animals in open water.
The name Setebos
The species epithet setebos comes from Setebos, a god in the mythology of the Tehuelche people of Patagonia. This name reaches wider audiences through Shakespeare's The Tempest, where Caliban's mother Sycorax worships Setebos as a deity from the extremities of the world. A fitting name for an animal that lives at the edge of the inhabitable planet.
How it compares to the Giant Pacific Octopus
The Giant Pacific Octopus (Enteroctopus dofleini) is the most famous large octopus, with arm spans recorded beyond 4 m. In terms of total reach, it is longer. But by body mass, Megaleledone setebos is considered heavier, with a more compact, dense build suited to the crushing pressure of deep Antarctic water. They live in different oceans, different depth ranges, and different temperature regimes, so there is no competition between them.
For other deep-ocean cephalopods, see our guides to the Vampire Squid and the Wonderpus Octopus.
Three things that make Megaleledone setebos remarkable
- It is the only octopus known to specialise in Antarctic deep-shelf habitat, tolerating temperatures that would shut down the metabolism of most invertebrates.
- Its smooth skin sets it apart from almost every other known octopus, which typically have textured skin for active camouflage in shallow water.
- Its scientific name connects a living animal to Patagonian mythology and a 400-year-old Shakespeare play, via a chain of colonial-era natural history that stretches through Darwin's voyages in the same waters.
Giant Antarctic Octopus: frequently asked questions
What is the Giant Antarctic Octopus?
Megaleledone setebos is a large, smooth-skinned octopus living beneath the Southern Ocean ice at depths of 100 to 2,200 m. It is considered the heaviest octopus in the world by body mass and is one of the rarest-observed animals in the Kaught catalog, with fewer than four confirmed iNaturalist records.
What is the largest octopus in the world?
By arm span, the Giant Pacific Octopus holds the record at over 4 m. By body mass, Megaleledone setebos is the heaviest known octopus. Both hold genuine records in different measures.
Where does the Giant Antarctic Octopus live?
Under the ice shelves and rocky seafloor of the circumpolar Southern Ocean, at 100 to 2,200 m depth, in water at or below 0°C. It has been recorded across the entire Antarctic coastline and the sub-Antarctic island zones.
Is the Giant Antarctic Octopus venomous?
Yes. Like all octopuses, it delivers venom through its beak to subdue prey. The venom poses no practical threat to humans: the animal lives in unreachable depths, and no attack on a human has ever been recorded.
Why is it Legendary in Kaught?
Kaught's rarity tier measures how often a species is observed in the wild. Megaleledone setebos has fewer than four confirmed iNaturalist records worldwide, making it one of the lowest-observation animals in the entire catalog. That earns the top tier: Legendary, four diamonds.
What does it eat?
Fish, crustaceans and other cephalopods, ambushed and immobilised with venom on the Antarctic seafloor in near-total darkness. Wide arm webbing helps the octopus engulf prey before it can escape.
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Species data, type, rarity tier and measurements, is drawn from the Kaught catalog, built on open biodiversity records from GBIF and iNaturalist. Rarity reflects how often a species is observed in the wild, not its conservation status.