The surface dwelling nudibranch, "Glaucus atlanticus" is a specialist predator of jellyfish, such as the Portuguese Man o' War. This predatory mollusc sucks air into its stomach to keep it afloat and using its muscular foot it clings to the surface film. If it finds a small victim "Glaucus" simply envelops it with its large mouth, but if the prey is a larger siphonophore the mollusc nibbles off its fishing tentacles, the ones carrying the most potent nematocysts. Like some others of its kind "Glaucus" does not digest the nematocysts; instead, it uses them to defend itself by passing them from its gut to the surface of its skin.