Pulmonates (Pulmonata) are an informal group of gastropods that include air-breathing snails and slugs. Most pulmonates are terrestrial or freshwater species, although there are a few marine species as well.
Pulmonates differ from other mollusks in their method of breathing. Over the course of their evolution, their gills have been replaced by a lung that has developed in the mantle cavity. The mantle cavity wall, which forms the lung sack (also called a pallial lung), has become highly vascularized (full of blood vessels).