 Sea snails are a very large group of animals and a very diverse one.Most snails that live in salt water respire using a gill or gills; a few species, though, have a lung, are intertidal, and are active only at low tide when they can move around in the air.These air-breathing species include false limpets in the family Siphonariidae and another group of false limpets in the family Trimusculidae.