In 2014, a careful DNA and anatomical study of the genus unexpectedly revealed the presence of a species complex. Only one species was found in the Atlantic, but the name Glaucus marginatus was revealed to include four separate species (referred to informally as the 'marginatus' clade). There are three species in the North Pacific Subtropical Gyre System and another species in the South Pacific Subtropical Gyre System. Glaucus atlanticus also occurs throughout the Indo-Pacific as well as in the Atlantic Ocean. In the North Pacific are Glaucus marginatus, Glaucus thompsoni and Glaucus mcfarlanei, with Glaucus marginatus also occurring in the Indian Ocean and the South Pacific. Also in the South Pacific is Glaucus bennettae.
