Latin Name: Macropinna microstoma
Geographic Location: North Pacific Ocean
Depth: 600-1000 meter
Size: 4 cm

The Pacific Barrel Eye, Macropinna microstoma, is the only species of fish in the genus Macropinna, belonging to the family Opisthoproctidae. It is instantly recognizable by its extremely unusual transparent, fluid-filled dome on its head. The lenses of its eyes can be seen through the transparent dome. Its barrel shaped eyes (hence its name) are set in the transparent dome and can be rotated to point straight up or forward. The Barrel Eye has a small mouth and with the exception of the transparent dome is mostly covered in large scales. The fish typically positions itself motionless in mid-water waiting for prey to swim into sight. In the low light conditions it is assumed the fish detects prey by their silhouette. Although very little is known about the behaviour and ecology of the barrel eye it has once been observed that when prey is detected, the eyes rotate like binoculars, facing forward as it turns its body from a horizontal to a vertical position to feed. The Barrel Eye was discovered in 1939, but was not seen alive until 2004 where the presence of the fragile transparent dome became apparent.