Glaucus

Glaucus is a genus of small blue pelagic sea slugs. They are aeolid nudibranchs, ranging in size from 20 to 40 mm. They feed on colonial cnidarians such as Portuguese men o' war, blue buttons, and purple sails. They can produce painful and potentially dangerous stings when handled, as they store the venomous nematocysts of their prey. Glaucus is the only genus in the family Glaucidae. It includes five species.