What Is the Glass Octopus and Why Can You See Through Its Body?

What Is the Glass Octopus?

The glass octopus (Vitreledonella richardi) is a deep-sea cephalopod whose body is almost entirely transparent, making its internal organs — including its eyes, optic nerves, and digestive tract — visible straight through its tissue.

A Ghost Built by Evolution

In the open ocean, there is no seafloor to hide beneath and no coral reef to duck behind. Animals that live in this vast, featureless environment — known as the mesopelagic and bathypelagic zones — face a unique survival problem: anywhere can be seen from any direction. The glass octopus evolved one of nature’s most elegant solutions. Rather than developing camouflage that blends into a background, it simply eliminated most of its visible body altogether. Its mantle, arms, and webbing are made of tissue so optically clear that light passes through with almost no distortion, rendering the animal functionally invisible to predators and prey alike.

The Eyes That Hide Themselves

The most striking anatomical feature of Vitreledonella richardi is its eyes. Unlike the round eyes of most octopuses, the glass octopus has elongated, tubular, rectangular eyes — and they rotate continuously to keep the dark, pigmented pupils oriented horizontally at all times. This is a specific adaptation to prevent the silhouette of its pupils from being detected by predators watching from below. The pupils are the one part of the animal that cannot be made transparent, so instead they are oriented to minimize their visible profile against the faint light filtering down from above.

A Century of Mystery

Scientists first formally described the glass octopus in 1918. For more than a hundred years after that, almost everything researchers knew about the species came not from direct observation but from partially digested fragments recovered from inside the stomachs of predatory fish and other marine animals. Live specimens were extraordinarily rare on film, and deep-sea trawling tends to destroy soft-bodied animals. The glass octopus remained one of the ocean’s most enigmatic creatures — known to exist, but almost never seen.

The 2021 Breakthrough

In 2021, the Schmidt Ocean Institute’s research vessel Falkor conducted a 34-day expedition to the Phoenix Islands Protected Area in the central Pacific Ocean. Using a remotely operated vehicle (ROV) equipped with high-definition cameras, the team captured more continuous live footage of glass octopuses than had been recorded across all previous decades combined. The footage revealed the animal’s behavior, movement, and anatomy in detail that had never before been documented, offering scientists their clearest look yet at one of the ocean’s most elusive inhabitants.

How Big Is the Glass Octopus?

Adult glass octopuses reach approximately 45 centimetres (about 18 inches) in total length. Despite their ghostly, delicate appearance, they are active hunters in the open water column, feeding on small fish, crustaceans, and other invertebrates. Their transparency is not fragility — it is precision engineering refined over millions of years of evolution.

Why It Matters

The glass octopus is a vivid reminder that the deep ocean remains one of the least explored environments on Earth. A species can be scientifically named for over a century and still be almost completely unknown in life. The Falkor expedition demonstrated that dedicated deep-sea exploration with modern ROV technology can reveal creatures that have been hiding from science in plain sight — and there are almost certainly many more waiting to be found.