its stomach, G. atlanticus floats at the surface. Due to the location of the gas sac, this species floats upside down. The upper surface is actually the foot (the underside in other slugs and snail), and this has either a blue or blue-white coloration. The true dorsal surface (carried downwards in G. atlanticus) is completely silver-grey. This coloration is an example of countershading, which helps protect it from predators that might attack from below and from above. The blue coloration is also thought to reflect harmful UV sunlight. Distribution and habitat This nudibranch is pelagic, and there is some evidence that it occurs throughout the world's oceans, in temperate and tropical waters. It has been recorded from the east and south coasts of South Africa, European waters, the east coast of Australia, and Mozambique. The G. atlanticus species geographical range increased northward by 150 km in the Gulf of California. Since the middle of the 19th century, records of this species have been reported on the Azores. Glaucus atlanticus was recently found in the Humboldt Current ecosystem in Peru in 2013, and off Andhra Pradesh in India in 2012. This is in line with the known habitat characteristics of the species: they thrive in warm temperate climates in the Southern Pacific, and in circumtropical and Lusitanian environments. Before finding G. atlanticus off Andhra Pradesh, these nudibranchs were documented as having been seen in the Bay of Bengal and off the coast of Tamil Nadu, India, over 677 kilometers apart. Glaucus atlanticus was also recently found off Bermuda in January 2016, and uncommonly washes ashore on east coast beaches at Barbados, Lesser Antilles. Although these sea slugs live on the open ocean, they sometimes accidentally wash up onto the shore, and therefore they may be found on beaches. In April 2022, specimens were found in the Gulf of Mexico along the Texas coast. Life history and behavior Glaucus atlanticus preys on other larger pelagic organisms. The sea slugs can move toward prey or mates by using their cerata to make slow swimming movements. They are known to prey on the dangerously venomous Portuguese man o' war (Physalia physalis); the by-the-wind-sailor (Velella velella); the blue button (Porpita porpita); and the violet snail, Janthina janthina. Occasionally, individuals attack and eat other individuals in captivity. The species is able to feed on the Portuguese man o' war due to its immunity to the venomous