Stylommatophora is an order[3] of air-breathing land snails and slugs, terrestrial pulmonate gastropod molluscs. This taxon includes most land snails and slugs. Stylommatophorans lack an operculum, but some close their shell apertures with temporary "operculum" (epiphragm) made of calcified mucus. They have two pairs of retractile tentacles, the upper pair of which bears eyes on the tentacle tips. All stylommatophorans are hermaphrodites.
The two strong synapomorphies of Stylommatophora are a long pedal gland placed beneath a membrane and two pairs of retractile tentacles.[4]
Stylommatophora are known from the Cretaceous period up to the present day.[5] A molecular clock estimate puts the origin of the crown group also to the Cretaceous.[6]
The most up-to-date formal classification of Stylommatophora is that of Bouchet et al. (2017).[3] Continuously updated information may be found at MolluscaBase.[7] The 2017 system already becomes obsolete in some parts due to new phylogenetic studies.
Rhytidoidea is apparently not a monophyletic group, but rather a collection of lineages from the southern hemisphere with unresolved relationships.[8]
According to the taxonomy of the Gastropoda by Bouchet & Rocroi (2005) based on evolutionary ancestry, Stylommatophora is a clade in the clade Eupulmonata within informal group Pulmonata.[9] It uses unranked clades for taxa above the rank of superfamily (replacing the ranks suborder, order, superorder and subclass) and the traditional Linnaean approach for all taxa below the rank of superfamily.