Blue angles of the sea, also known as Glaucilla marginata is a species of small, floating, blue sea slug.
Glaucus atlanticus is a species of small-sized blue sea slug, a pelagic aeolid nudibranch, a marine gastropod mollusk in the family Glaucidae. It is closely related to Glaucilla marginata, which is sometimes included in Glaucus. Wikipedia
They live and move beneath the surface of the water, being kept by surface tension or, in extreme cases, swallows air bubbles.