The Pacific Barreleye fish gets its name from large eyes that are literally shaped like barrels, topped with beautiful green lenses. Also known as the Macropinna microstoma, its head is completely transparent, filled with fluid. This unique creature lives at depths of around 2000 to 2,600 ft. The Pacific Barreleye’s see-through head may seem weird, but it has a very clear purpose –  to help it see better in the dark waters that it inhabits.

The Barreleye’s eyes have been found to be incredibly sensitive, snapping up any stream of light available. Unlike most other fish, both the eyes are in the front of the head and point in the same direction, which gives it amazing binocular vision. So the Barreleye is able to spot faint objects that other fish cannot, making it a feared predator. It’s extremely fascinating, how it searches for prey. It starts off by staying still, eyes pointed upward in search of prey. Sometimes the eyes are rotated to face forwards, or the eyes are still and the body is rotated so that the mouth is pointing in the same direction as the eyes. When tiny silhouettes of prey are spotted, the Barreleye moves in exactly the same direction to catch them. Its flat, horizontal fins help it to swim very precisely. This method is so efficient that it is sometimes able to even snatch food away from the stinging tentacles of other deep sea creatures. Its mouth is really tiny so that’s of great help as well, and the transparent shield makes it immune to stings.

The Pacific Barreleye was discovered in 1939, but it hasn’t been spotted alive since 2004 off California’s central coast by the Monterey Bay Aquarium Research Institute (MABRI). Its biological system apparently has flaws; it is said to be rather sensitive to pressure. When fished up, it’s head would shatter somewhere along the way and only mangled specimens would come up in the nets. MABRI was successful in finding the only such fish with its soft dome intact, measuring about 6 inches in length.

 Photos & video: National Geographic