A giant isopod is any of the almost 20 species of large isopods (crustaceans distantly related to the shrimp and crabs, which are decapods) in the genus Bathynomus. They are thought to be abundant in cold, deep waters of the Atlantic, Pacific and Indian Oceans.] Bathynomus giganteus, the species upon which the generitype is based, is often considered the largest isopod in the world, though other comparably poorly known species of Bathynomus may reach a similar size.