Glaucus atlanticus (common names include the blue sea dragon, sea swallow, blue angel, blue glaucus, dragon slug, blue dragon, blue sea slug and blue ocean slug) is a species of small, blue sea slug, a pelagic (open-ocean) aeolid nudibranch, a shell-less gastropod mollusk in the family Glaucidae. These sea slugs are pelagic; they float upside down by using the surface tension of the water to stay up, where they are carried along by the winds and ocean currents. G. atlanticus makes use of countershading: the blue side of their body faces upwards, blending in with the blue of the water. The silver/grey side of the sea slugs faces downwards, blending in with the sunlight reflecting on the ocean's surface when viewed facing upwards underwater. Glaucus atlanticus feed on other pelagic creatures, including the Portuguese man o' war and other venomous siphonophores. This sea slug stores stinging nematocysts from the siphonophores within its own tissues as defence against predators. Humans handling the slug may receive a very painful and potentially dangerous sting. Taxonomy This species looks similar to, and is closely related to, G. marginatus, which is now understood to be not one species, but a cryptic species complex of four separate species that live in the Indian Ocean and Pacific Ocean. It shares the common name "blue dragon" with Pteraeolidia ianthina and G. marginatus. Description At maturity G. atlanticus can be up to in length, though larger specimens have been found. It can live up to a year under the right conditions. It is silvery grey on its dorsal side and dark and pale blue ventrally. It has dark blue stripes on its head. It has a flat, tapering body and six appendages that branch out into rayed, finger-like cerata. Cerata, also known as papillae, extend laterally from three different pairs of peduncles. The papillae are placed in a single row (uniseriate) and may be up to 84 inches total, (Forster, 1777). Glaucus atlanticus is usually found in tropical/subtropical areas, floating at the ocean's surface due to the stored gulped air inside their stomachs. They usually feed on cnidarians, which can be noisy due to air escaping their stomachs as they feed. The radula of this species bears serrated teeth which, paired with a strong jaw and denticles, allows it to grasp and "chip down" parts of its prey. Buoyancy and coloration With the aid of a gas-filled sac in