This species looks similar to, and is closely related to, G. marginatus, which is now understood to be not one species, but a cryptic species complex of four separate species that live in the Indian and Pacific Oceans. It … See more

At maturity, G. atlanticus is usually around 3 cm (1.2 in) in length, though larger specimens have been found. It can live up to a year under the right conditions. It is silvery grey on its dorsal side and dark and pale blue v… See more

With the aid of a gas-filled sac in 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 … See more

This nudibranch is pelagic, and some evidence indicates 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 … See more

G. atlanticus preys on other larger pelagic organisms. The sea slugs can move toward prey or mates by using their cerata, the thin feather-like "fingers" on its body, to make slow swimming movements. They are known to pr… See more