Glaucus atlanticus, commonly known as the blue dragon, is a species of sea slug in the family Glaucidae. It is pelagic and found in tropical and temperate oceans worldwide. The species floats upside down at the ocean's surface using a gas-filled sac in its stomach, with blue and silver countershading to help camouflage it from predators. It preys on venomous cnidaria such as the Portuguese man o' war, storing the prey's stinging nematocysts in specialised sacs for its own defence. Handling the slug can result in a painful sting and symptoms such as nausea and allergic contact dermatitis. This G. atlanticus sea slug, about 35 millimetres (1.4 in) in length, was found washed up on a beach at Surfers Paradise in Queensland, Australia.

Photograph credit: Taro Taylor