The Glaucus atlanticus is a brightly colored sea slug found all over the world in tropical and temperate oceans. Also called 'blue dragon' or 'sea swallow', the species absorbs toxic chemicals and stinging cells from its prey into its own body. Such toxins are incorporated into the glaucus' skin giving the slug a potent defense mechanism against predators. Their favorite food is the Portuguese man o' war, who provide the slugs with an abundance of stinging cells called nematocysts.
These are stored and concentrated, so that when the blue glaucus is threatened, it can release a sting much more potent than the man o' war itself. These defensive capabilities are important, as the species is quite small, reaching a maximum length of only 3 centimeters. Not content to roam along the seafloor, these nudibranchs float around in the water using air bubbles trapped in their stomachs. When floating near the surface, they often float upside-down, to expose their brightly colored bellies to any potential predators above.
The bright blue blends in with the surrounding water, while their grey backs hide them from below - this evolutionary camouflage technique is called 'countershading'.Like all sea slugs, the blue glaucus is a hermaphrodite, producing both eggs and sperm. The eggs, which are long, and spiraled are released into the water where they can only be fertilized by the sperm of another individual.