# 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.

## Taxonomy
### 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 Anostomopsidae
** 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)