Glaucus atlanticus (common names sea swallow, blue glaucus, blue dragon, blue sea slug and blue ocean slug) is a species of small-sized blue sea slug, a pelagic aeolid nudibranch, a marine gastropod mollusk in the family Glaucidae. This is the only species in the genus Glaucus, but is closely related to Glaucilla marginata, which sometimes is included in Glaucus.
The normal size of this species is up to about 3 cm, depending on the animal's age. It is silvery grey on its dorsal side and dark and pale blue ventrally. It has dark blue stripes on its face. It has a tapering body which is flattened and has six appendages which branch out into rayed cerata. Its radula bears serrated teeth on their blades.
VIDEO OF Glaucus atlanticus .