Brownsnout Spookfish

The brownsnout spookfish is the only known vertebrate to use both refractive lenses and reflective mirrors to focus light in its eyes. While its main tubular eyes use lenses to look upwards, its diverticular eyes use curved, mirrored plates to focus faint light from below. This unique anatomy allows it to spot the silhouettes of predators and prey in the deep sea.

This species is a mesopelagic fish, meaning it lives in the twilight zone of the ocean, typically found at depths between 500 and 2,400 meters. They are widely distributed across the tropical and subtropical waters of the Atlantic, Pacific, and Indian Oceans. They migrate to shallower waters at night to feed on small crustaceans.

The brownsnout spookfish is relatively small, with adults generally reaching a maximum length of about 18 centimeters (roughly 7 inches). Despite its small size, it has a specialized, heavily armored skull to protect its highly sensitive optical organs. It also features a transparent dome over its head to allow light to reach its tubular eyes.

The species was first scientifically described in 1888 by the German zoologist Albert Günther. It belongs to the barreleye family, known scientifically as Opisthoproctidae. Its unique, mirror-based optical anatomy wasn't fully understood by scientists until detailed studies were conducted over a century later.