How can a fish look through its own skull? Off the coast of Monterey Bay, a team of researchers found themselves unexpectedly crossing paths with the barreleye, that deep-sea creature with a transparent head. Scientists were “fascinated” by observing Macropinna microstoma at a depth of 600 meters.
- MBARI researchers observed a barreleye (Macropinna microstoma) at 600 meters depth in Monterey Bay during a mission initially devoted to gelatinous animals.
- This fish has a transparent dome-shaped head housing two green rotating eyes, allowing it to direct its gaze to spot prey in the dim depths.
- The animal remained motionless facing the camera for about 20 minutes, an exceptional duration that allowed scientists to photograph it from all angles, while the mystery of the exact function of its eyes remains unresolved.
- A Glass Head and Pivoting Eyes: The Barreleye’s Unusual Anatomy
- Twenty Minutes in Front of the Camera: The Encounter That Surprised Seasoned Researchers
- Seeing Without Being Seen: The Still-Unsolved Mystery of Its Fluorescent Green Eyes
A Glass Head and Pivoting Eyes: The Barreleye’s Unusual Anatomy
The barreleye, scientifically named Macropinna microstoma, belongs to those animals you don’t forget once you’ve seen them. Its head is covered by a transparent dome, like a glass bubble resting atop its skull. Inside this capsule, two large green, globe-like eyes can rotate freely.
This anatomical peculiarity would allow it to orient its gaze as needed, a trait that contributes to its singular appearance among deep-sea creatures.
The species lives in the twilight zone, a layer of water roughly between 200 and 1,000 meters deep. There, sunlight fades quickly, giving way to a cold, dark universe where every adaptation matters for survival.
Facing such extreme conditions, Macropinna microstoma has developed flat fins that help it stay motionless for extended periods, waiting for prey to come within reach of its rotating eyes.
Twenty Minutes in Front of the Camera: The Encounter That Surprised Seasoned Researchers
It all began during a mission dedicated to an entirely different subject. Scientists from the Monterey Bay Aquarium Research Institute (MBARI) were scanning offshore waters aboard the research vessel David Packard to study gelatinous animals like jellyfish, siphonophores, and ctenophores.
This eight-day expedition, named “Deep Dive for Fragile Gelatinous Life,” took them about 90 kilometers offshore, with the remotely operated vehicle Doc Ricketts at their disposal. The objective was to understand how gelatinous creatures adapt to life in the depths.
But just as the team was about to rise to the surface, at around 600 meters depth, a very different face appeared on the ROV’s cameras. The sight startled everyone, to the point that several team members were already back in the laboratory cataloging their samples.
“It’s always a pleasure to stumble upon a fish as rare and unique as this one,” said Kyra Schlining, a research specialist at MBARI, to IFLScience. She notes that the last observation of the genus went back to 2021, before ROVs were equipped with 4K cameras.
Usually, these fish reveal themselves only for a few minutes before slipping back into the darkness. This specimen stayed in front of the lens for nearly 20 minutes, giving researchers the chance to photograph it from every angle.
Seeing Without Being Seen: The Still-Unsolved Mystery of Its Fluorescent Green Eyes
The unusually green tint of the barreleye’s eyes has intrigued scientists for a long time. The most widely held hypothesis is that it helps distinguish natural light from bioluminescent light, enabling it to better detect prey against the downwelling light of the deep sea.
But for Steven Haddock, MBARI senior scientist, this explanation does not fully account for all of it. “There are hypotheses about the function of the transparent dome and of its rotating tubular eyes, but I think we still do not know exactly what it is looking for to detect its prey,” he told IFLScience.
He also questions the precise role of the green pigmentation in the lenses and poses a question that nicely sums up the creature’s mystery: “What does the world look like through its eyes?”
What particularly impressed Haddock during this encounter was the fish’s calm demeanor. “I love the calm of the fish, almost as if it were filmed in slow motion,” he explained. He contrasts this behavior with that of other deep-sea predators, such as dragonfish, which freeze for a few seconds before bolting away.
This time, the 20 minutes in view allowed the team to test different lighting angles, and even position the animal before a virtual reality camera—a luxury rarely granted by this ghostly face of the deep.
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Source: MBARI
