The Crepusculans were a non-humanoid species. They possessed three pairs of appendages, of which the front two arms ended in three tendril-like fingers. Their two-eyed heads sported further tendrils, and their forked tail was similarly tendril-like. Their young grew in large egg sacs.
As of the mid-23rd century, their species was contained on an arid world on which they had been living for over a thousand years. In 2256, ambient radiation from a meteor mining accident threatened to cause an eighty-nine-year drought on the world, which would render them extinct within a thousand hours. Captain Philippa Georgiou and Lieutenant Commander Michael Burnham of the USS Shenzhou covertly visited the planet and restored their water supply.