A strange spider with glowing eyes that lived more than 100 million years ago was discovered by paleontologists working in South Korea.

Eleven spiders dating to the Cretaceous period were preserved in shale on the Korean peninsula, Live Science reports. Two of them contain traces of eerily sparkling eyes, known as "tapetums," which bounce light from the back of the eye through the retina.

"ln spiders, the ones you see with really big eyes are jumping spiders, but their eyes are regular eyes — whereas wolf spiders at nighttime, you see their eyes reflected in light like cats," study co-author Paul Selden, director of the Paleontological Institute at the University of Kansas Biodiversity Institute and Natural History Museum, said in a statement. "So, night-hunting predators tend to use this different kind of eye. This was the first time a tapetum had been in found in fossil."

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According to Seldon, the rocks where the spiders were found also contained the remnants of tiny fish and crustaceans.

The spiders lived between 110 and 113 million years ago and were somehow protected from decay to remain so well-preserved, researchers said.

The researchers' findings were published in the Journal of Systematic Palaeontology.

"These spiders were doing things differently. ... It's nice to have exceptionally well-preserved features of internal anatomy like eye structure. It's really not often you get something like that preserved in a fossil," Selden said in his statement.