When is a shark not a shark? When it’s a ghost shark! These creatures are actually chimaeras—cartilaginous fishes that are related to sharks but distinguished by several differences, including having only one gill on either side of the body. Inhabitants of deep water, chimaeras can grow more than six feet long depending on the species. Their eyes are backed with a reflective tissue layer that makes them seem to glow in the dark, contributing to an eerie—even ghostlike—appearance. This video gives you a rare glimpse of a ghost shark swimming around on a seamount.