These deep-dwelling fish can see through their own foreheads.
Even in a world full of adaptations for seeing in near-total darkness, the barreleye fish (Macropinna microstoma) stands out as one of the most bizarre. Two small indentations where eyes might normally appear on a fish are actually the barreleye’s olfactory organs, and its eyes are two glowing green orbs behind its face that gaze up towards the top of its head.
In 2009, MBARI researchers showed that the fish can rotate its eyes towards the front to see its food when eating. Before that, scientists believed that the barreleye’s gaze was fixed looking straight up. Researchers think that the fish hovers below a siphonophore’s tentacles to steal food.
Maximum size: 15 centimeters (6 inches)
Depth: 600–800 meters (2,000–2,600 feet)
Range: Bering Sea to Japan and Baja California
Diet: zooplankton, including crustaceans and siphonophores