This group includes land snails and land slugs, however loss of the shell has taken place many times in different groups that are not evolutionarily closely related, and in specialized malacological literature, land snails and slugs are most often treated together as one group.
All terrestrial molluscs belongs to the class Gastropoda, however colonization of the land took place several times during the evolutionary past, and as a result terrestrial molluscs are classified in several different, often not closely related, gastropod taxa.
Terrestrial mollusks comprise about 35 thousand species, most of which belong to the order (in some sources suborder or infraorder) Stylommatophora.
According to an estimate from Cameron, of the 409 existing gastropod families there are 119 families which include terrestrial molluscs. Among these families, 104 are Stylommatophora, 7 are terrestrial pulmonates other than stylommatophorans, and 8 are operculates (formerly "prosobranchs", molluscs with an operculum, a group that primarily consists of marine snails).
- Cyclophoroidea (up to 10 families in different classifications)
- Pomatiidae (in the superfamily Littorinoidea, which consist mainly of marine snails)
- Amphiboloidea (three families of land and semi-marine snails)
- Ellobioidea (or Actophila) (1-5 families in different classifications, some of the species live in litoral both in marine and terrestrial habitats)
- Systellommatophora (3 families of land and semi-marine slugs)
- Stylommatophora (more than 100 families of land snails and slugs)
Best known terrestrial malacologists
- Oskar Boettger
- Jacques Philippe Raymond Draparnaud
- Wilhelm Kobelt
- Henry Augustus Pilsbry
- Emil Adolf Rossmässler
- Heinrich Simroth
- Carl Agardh Westerlund
- Barker G. M. (ed.) The biology of terrestrial molluscs. CABI Publishing, 2001, 558 pp. ISBN 0-85199-318-4.
- Barker G. M. (ed.) Natural enemies of terrestrial molluscs. CABI Publishing, 2004, 644 pp. ISBN 0-85199-319-2.
- Cameron R. Slugs and snails. HarperCollins Publishers, London, 2016, 508 pp. ISBN 978-0-00-711301-9.