The Glaucus atlanticus
, or blue glaucus (Forster, 1777) is the only species of the genus Glaucus
and only one of two species in the family Glaucidae
.The animals float upside down at the surface of the sea, keeping afloat by swallowing air which is stored in their stomachs.Their diet is mainly made up of hydrozoans including the Portuguese Man o’ War - they even eat the stings. As well as getting nourishment from the stings, they use them for their own defence.