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Pulmonata (phylum Mollusca, class Gastropoda) A subclass of mainly terrestrial gastropods, with some aquatic members, in which the anterior mantle cavity is modified into a lung. A few have small, secondary gills. The head usually has one or two pairs of tentacles. The foot generally occupies the entire ventral surface, forming a flat, creeping sole. The shell, if present, can be quite variable in shape. Members of only one family have an operculum. Individuals are hermaphroditic. The subclass first appeared in the Mesozoic.