(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.
Subjects: Zoology and Animal Sciences.