Glaucus atlanticus, commonly known as the sea swallow, blue angel, blue glaucus, blue dragon, blue sea slug, or blue ocean slug is a small blue sea slug, a gastropod mollusk in the family Glaucidae. They feed on other pelagic creatures, including the venomous Portuguese Man o’ War. The glaucus atlanticus stores stinging nematocysts from the Man o’ War in its own tissues, a human picking one up may receive a painful sting.