Distribution and habitat
This nudibranch is pelagic, and is distributed throughout the world's oceans, in temperate and tropical waters. Regions where this slug is found include the East and South Coast of South Africa, European waters, the east coast of Australia and Mozambique. This species floats upside down on the surface tension of the ocean.
With the aid of a gas-filled sac in its stomach, Glaucus atlanticus floats at the surface. Due to the location of the gas sac the sea swallow floats upside down. The dorsal surface, actually the foot and underside, has either a blue or blue-white coloration. The true dorsal surface is completely silver-grey. This coloration is an example of counter shading, which helps protect it from predators from below, sides and above.
Feeding on the "By-the-wind sailor" (Velella velella). Also feeds on the Portuguese man-o'-war, commonly
known as the Bluebottle (Physalia physalis) and, below, on Porpita porpita.
Mating sequence shown below