The blue dragon sea slug, Glaucus atlanticus, is a captivating marine creature that often sparks curiosity with its unique appearance. This small, iridescent mollusk is a type of nudibranch, a group of shell-less sea snails known for their often vibrant coloration. This fascinating animal drifts through the ocean, showcasing adaptations that allow it to survive in its open-water environment.
The Blue Dragon’s True Size
The blue dragon sea slug is notably small, typically reaching about 3 centimeters (1.2 inches) in length at maturity. Some individuals have been observed to grow slightly larger, up to 3.5 centimeters, and in rare cases, even up to 6 centimeters. To visualize its size, imagine a creature no bigger than a typical paperclip or a small button. This diminutive stature allows it to remain largely unnoticed as it floats on the ocean’s surface.
Its Striking Appearance
This sea slug possesses a distinctive flattened, tapering body adorned with vibrant blue and silver coloration. Its ventral side, which faces upwards as it floats, is typically dark and pale blue, often with dark blue stripes on its head. From its body extend six finger-like appendages called cerata, which branch out from three pairs of peduncles. This unique coloration acts as countershading, where the blue upper side blends with the water’s surface to camouflage it from aerial predators. Conversely, its silvery-grey underside faces downwards, blending with the bright surface reflection when viewed from below by aquatic predators.
Where These Sea Slugs Live
The blue dragon sea slug is a pelagic species, meaning it inhabits the open ocean rather than coastal or seabed environments. It can be found floating on the surface of tropical and temperate waters across the Atlantic, Pacific, and Indian Oceans. This creature relies entirely on ocean currents and winds for its movement, passively drifting across vast expanses. Occasionally, strong winds can carry these sea slugs, sometimes in groups known as “blue fleets,” onto beaches where they become stranded.
Beyond Its Looks: Unique Adaptations
The blue dragon sea slug possesses specialized adaptations. It primarily feeds on venomous siphonophores, such as the Portuguese man o’ war, which are colonial organisms related to jellyfish. The blue dragon is able to consume these venomous prey without being harmed, instead absorbing and storing their stinging cells, known as nematocysts, from its prey, which are then used for its own defense, stored within the tips of its cerata. A sting from a blue dragon sea slug can be painful to humans, with symptoms similar to those caused by a Portuguese man o’ war. To maintain its position floating upside down at the surface, the blue dragon sea slug swallows an air bubble for buoyancy.