The Blue Glaucus (Glaucus atlanticus) is a species of brightly colored sea slug that is normally found in temperate and tropical waters. Like most sea slugs, this species incorporates toxic chemicals or stinging cells from its prey into its own skin. This ability provides the blue glaucus with a defense mechanism against predators.
Despite its arsenal of defenses, the blue glaucus rarely reaches more than 3 centimeters long. And unlike most benthic sea slugs, this species lives throughout the entire water column. An air bubble stored in its stomach keeps the nudibranch afloat. The creature often floats on its backside, showing its brightly colored underbelly to airborne predators. The bright blue color acts as camouflage against the backdrop of ocean waves while the animal’s grayish backside blends with the bright sea surface, concealing it from predators below.
Like other sea slugs, the blue glaucus isn’t venomous by itself. When feeding on its preferred prey, Portuguese man o’ wars, the blue glaucus stores the stinging nematocysts created by the prey’s notoriously long, venomous tentacles — these tentacles may average up to 30 feet long! The stinging cells are stored and concentrated for the future, so when the blue glaucus is threatened or touched, it can release these stinging cells to deliver a far more potent sting than the Portuguese man o’ war can alone.
Like most small marine invertebrates, little is known about the conservation status of the blue glaucus, especially given the species’ pelagic lifestyle in the open ocean.