The barreleye lives more than 2,000 feet (600 meters) beneath the ocean's surface, where the water is almost inky.

The transparent-headed fish spends much of its time motionless, eyes upward, MBARI scientists discovered while watching the barreleye fish from a remotely operated vehicle.

The green lens atop each of the fish's eyes filters out what little sunlight makes it down from the surface, allowing the fish to focus on the bioluminescence of small jellies or other prey passing overhead.

Then the eyes rotate forward to follow the prey, allowing the fish to home in on its meal.