Sigmurethra

Sigmurethra is a taxonomic category of air-breathing land snails and slugs, terrestrial pulmonate gastropod molluscs. This is an informal group which includes most land snails and slugs.

The two strong synapomorphies of Sigmurethra are a long pedal gland placed beneath a membrane and retractile tentacles.

Several families in this group contain species of snails and slugs that create love darts.

Sigmurethra are known from the Cretaceous to the Recent periods.

2005 Taxonomy
In the taxonomy of the Gastropoda by Bouchet & Rocroi, 2005, Sigmurethra is an "Informal Group", a subsection of the Stylommatophora. It consists of the following families:
 * Superfamily Clausilioidea
 * Family Clausiliidae
 * † Family Anadromidae
 * † Family Filholiidae
 * † Family Palaeostoidae
 * Superfamily Orthalicoidea
 * Family Orthalicidae
 * Family Cerionidae
 * Family Coelociontidae
 * † Family Grangerellidae
 * Family Megaspiridae
 * Family Placostylidae
 * Family Urocoptidae
 * Superfamily Achatinoidea
 * Family Achatinidae
 * Family Ferussaciidae
 * Family Micractaeonidae
 * Family Subulinidae
 * Superfamily Aillyoidea
 * Family Aillyidae
 * Superfamily Testacelloidea
 * Family Testacellidae
 * Family Oleacinidae
 * Family Spiraxidae
 * Superfamily Papillodermatoidea
 * Family Papillodermatidae
 * Superfamily Streptaxoidea
 * Family Streptaxidae
 * Superfamily Rhytidoidea
 * Family Rhytididae
 * Family Chlamydephoridae
 * Family Haplotrematidae
 * Family Scolodontidae
 * Superfamily Acavoidea
 * Family Acavidae
 * Family Caryodidae
 * Family Dorcasiidae
 * Family Macrocyclidae
 * Family Megomphicidae
 * Family Strophocheilidae
 * Superfamily Plectopyloidea
 * Family Plectopylidae
 * Family Corillidae
 * Family Sculptariidae
 * Superfamily Punctoidea
 * Family Punctidae
 * † Family Anastomopsidae
 * Family Charopidae
 * Family Cystopeltidae
 * Family Discidae
 * Family Endodontidae
 * Family Helicodiscidae
 * Family Oreohelicidae
 * Family Thyrophorellidae
 * Superfamily Sagdoidea
 * Family Sagdidae

limacoid clade

 * Superfamily Staffordioidea
 * Family Staffordiidae
 * Superfamily Dyakioidea
 * Family Dyakiidae
 * Superfamily Gastrodontoidea
 * Family Gastrodontidae
 * Family Chronidae
 * Family Euconulidae
 * Family Oxychilidae
 * Family Pristilomatidae
 * Family Trochomorphidae
 * Fossil taxa probably belonging to the Gastrodontoidea
 * Subfamily † Archaeozonitinae
 * Subfamily † Grandipatulinae
 * Subfamily † Palaeoxestininae
 * Superfamily Parmacelloidea
 * Family Parmacellidae
 * Family Milacidae
 * Family Trigonochlamydidae
 * Superfamily Zonitoidea
 * Family Zonitidae
 * Superfamily Helicarionoidea
 * Family Helicarionidae
 * Family Ariophantidae
 * Family Urocyclidae
 * Superfamily Limacoidea
 * Family Limacidae
 * Family Agriolimacidae
 * Family Boettgerillidae
 * Family Vitrinidae

Informal group Sigmurethra continued
Two superfamilies belongs to clade Sigmurethra, but they are not in the limacoid clade.
 * Superfamily Arionoidea
 * Family Arionidae
 * Family Anadenidae
 * Family Ariolimacidae
 * Family Binneyidae
 * Family Oopeltidae
 * Family Philomycidae
 * Superfamily Helicoidea
 * Family Helicidae
 * Family Bradybaenidae
 * Family Camaenidae
 * Family Cepolidae
 * Family Cochlicellidae
 * Family Elonidae
 * Family Epiphragmophoridae
 * Family Halolimnohelicidae
 * Family Helicodontidae
 * Family Helminthoglyptidae
 * Family Humboldtianidae
 * Family Hygromiidae
 * Family Monadeniidae
 * Family Pleurodontidae
 * Family Polygyridae
 * Family Sphincterochilidae
 * Family Thysanophoridae
 * Family Trissexodontidae
 * Family Xanthonychidae

(Families that are exclusively fossil are indicated with a dagger †)

New families after 2005

 * Superfamily Streptaxoidea
 * Diapheridae - In 2010, Sutcharit et al. (2010) established a new family Diapheridae within the Streptaxoidea.

2017 Taxonomy
After excluding groups not related, the informal group Sigmurethra becomes suborder Helicina, with the following nine infraorders and a collection of families with no superfamily：
 * Suborder Helicina ("Non-Achatinoid Clade")
 * Infraorder Arionoidei
 * Infraorder Clausilioidei
 * Infraorder Helicoidei: formed from Helicoidea Rafinesque, 1815 and Sagdoidea Pilsbry, 1895
 * Infraorder Limacoidei: formed from original limacoid clade
 * Infraorder Oleacinoidei
 * Oleacinoidea: formed from original Testacelloidea but with the family Testacellidae excluded;
 * Haplotrematoidea: formed from original Rhytidoidea and Haplotrematidae
 * Infraorder Orthalicoidei
 * Infraorder Pupilloidei (Orthurethra)
 * Infraorder Rhytidoidei: formed by Rhytidoidea merging with contents from Acavoidea.
 * Infraorder Succineoidei (Elasmognatha)