This Crazy Deep-Sea Fish Has a Completely Transparent Head

The barreleye fish looks like a model in a high school science classroom with a see-through portion to allow for an examination of the inner workings. But this is how the astonishingly bizarre fish naturally occurs—transparent head and all.

Though it was first discovered in 1939, little was known about Macropinna microstoma for the next 70 years. The only information about the fish, which lives 2000 to 2600 feet below the surface, came from damaged specimens caught in fishing nets, meaning scientists never saw an intact barreleye fish until recently. Depictions from the 20th century show the large, tubular eyes necessary to make use of limited sunlight, but they failed to show the fluid-filled dome that covers those unusual peepers.

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In 2009, the Monterey Bay Aquarium Research Institute (MBARI) was finally able to film the barreleye fish in its natural habitat using a remotely operated camera and captured a short-lived specimen for research purposes. This first-ever footage of the curious creature, seen below, revealed the transparent dome that covers and protects its eyes.

The two dark spots that look like eyes are actually part of the barreleye fish's olfactory system, and are akin to nostrils. Meanwhile, its eyes are the bright green orbs inside its head. In the video, they're pointing upward, scanning the water above for potential prey. Scientists had long wondered how the fish would actually feed if it is always looking perpendicular to where its mouth is, but MBARI researchers determined that the eyes can swivel within the clear dome to face forward if need be. The scientists speculate the barreleye fish hunts by stealing captured prey from massive jellies like siphonophores. The transparent head acts as a shield to protect the fish's eyes from the jelly's stinging tentacles as it snatches a snack with its small, precise mouth.