This cave-dwelling eel is going blind, by losing one eye at a time

Scientists exploring underwater caves have discovered a new species of moray eel that appears to be adapting to its unique habitat—by losing its eyes. Some specimens of Uropterygius cyamommatus have left eyes covered by skin, whereas others retain eyes on both sides of their heads.

The researchers used baited traps to lure the morays to the surface of inland caves that connect to the ocean on Australia’s Christmas Island and the Philippines’s Panglao Island. The fish are the first known species of moray to inhabit these formations, known as anchialine caves. Two of the four specimens the scientists collected had no visible left eye , they report in the Raffles Bulletin of Zoology .

Many of the nearly 300 species of cave-dwelling fish have lost their eyes entirely , but the cycloptic nature of U. cyamommatus is unusual—scientists appear to be capturing evolution in action. Eons ago, before they retreated to the inky depths of the caves, the ancestors of these eels may have needed their eyes to hunt and detect predators. But now, in the absence of light, eyes have become unnecessary—and too costly for the body to make. Instead, the eels likely rely on their sense of smell to locate passing prey in their turbulent, wave-crashed environment.