Viewed from afar, the guitarfish is a strange sight: with its long body and triangular head, the enormous ray looks a bit like a shark who swallowed a guitar. Up close, the guitarfish, a member of the Rhinobatidae family, looks even stranger. That’s because the giant fish doesn’t have eyelids. Instead, to protect itself from sand and debris, it retracts its eyes back into its head almost 1.6 inches.
In a recent study, published in Zoology, scientists announced their discovery of the muscle responsible for the guitarfish’s retractable eyes. Called the obliquus inferior, the muscle is attached to the underside of the fish’s skull, and allows the fish to pull its eyes backward into its head.
Scientists used a range of methods, from dissections to video recordings, to identify the specific muscle responsible for the fish’s strange eye movements. While digital recordings allowed them to measure the depth of the retractions, the biggest breakthrough came when scientists began electrically stimulating the eye muscles of dissected fish. They found that stimulation of the obliquus inferior caused the fish’s eyes to sink ventrally.
Guitarfish aren’t the only animals with retractable eyes: frogs, bottlenose dolphins, skates, and several other species also share that strange skill. However, the distance that guitarfish are able to retract their eyes is likely unique. “The eye retraction distance was nearly the same as the diameter of the eyeball itself, indicating that eye retraction in the giant guitarfish is probably one of the largest among vertebrates,” the study explains. Check out its strange ocular gymnastics, courtesy of Science Magazine, below.