(subclass Pulmonata), any of various land, freshwater, and marine snails belonging to the class Gastropoda (phylum Mollusca) that have lost their ancestral gills and breathe instead by means of a “lung”—a highly vascularized saclike modification of the mantle cavity. Some snails lack an external shell, but most pulmonates have a spiral shell that may be attenuated or flattened. They are anatomically more advanced than other snails: all are detorted (bilaterally symmetrical, with an unlooped nerve cord) as adults, and the auricle of the heart is anterior to the ventricle. All are hermaphroditic—i.e., with both male and female reproductive organs in one animal. In addition, pulmonates are used in the delicacy escargot.