Numerous eyeless animals, including the Kauai cave wolf spider, live in total darkness. Lack sight, other senses developed heightened sensitivities to compensate. As with other animals, such as blind cavefish, these spiders descended from ones with eyes.
The atavistic resurrection of complex ancestral traits, contrary to Dollo’s law, appears to be more frequent than commonly thought. ~ German zoologist Katja Domes et al