Heterobranchia, the heterobranchs (meaning "different gill"), is a taxonomic

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

snail A snail is a shelled gastropod. The name is most often applied to land snails, terrestrial molluscs, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class Gas ...

s and

slug Slug, or land slug, is a common name for any apparently shell-less Terrestrial mollusc, terrestrial gastropod mollusc. The word ''slug'' is also often used as part of the common name of any gastropod mollusc that has no shell, a very reduced ...

s, which includes marine, aquatic, and terrestrial

gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...

mollusc Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...

s. Heterobranchia is one of the main clades of gastropods. Currently Heterobranchia comprises two groups: the opisthobranchs, and the pulmonates.

Diversity

The two subdivisions of this large clade are quite diverse: * Opisthobranchia are virtually all marine species, some shelled and some not, and comprise about 25 families and 2000 species of the bubble shells, the seaslugs, as well as the sea hares. The internal organs of the opisthobranchs have undergone detorsion (unwinding of the viscera that were twisted during torsion). * The Pulmonata comprises about 20000 species, includes the majority of land snails and slugs, many freshwater snails, and a small number of marine species. The mantle cavity of the Pulmonata is modified into an air-breathing organ. They are also characterized by detorsion and a symmetrically-arranged nervous system. The pulmonates almost always lack an operculum and are hermaphroditic. Architectonica_perspectiva_S4-01

Taxonomy

Current taxonomy

Heterobranchia * Lower Heterobranchia ** Valvatoidea Gray, 1840 ** Architectonicoidea Gray, 1850 ** Mathildoidea Dall, 1889 ** Omalogyroidea G. O. Sars, 1878 ** Allomorpha *** Murchisonelloidea Casey, 1904 *** Rhodopoidea Ihering, 1876 ** Orbitestelloidea Iredale, 1917 ** Cimoidea Warén, 1993 *

Euthyneura Euthyneura is a taxonomic infraclass of snails and slugs, which includes species exclusively from marine, aquatic and terrestrial gastropod mollusks in the clade Heterobranchia. Euthyneura are characterised by several autapomorphies, bu ...

** Actenonacea *** Acteonoidea d'Orbigny, 1843 *** Rissoelloidea Gray, 1850 ** Tjaernoeiidae Warén, 1991 ** Ringipleura *** Ringiculoidea Philippi, 1853 *** Nudipleura **

Tectipleura Tectipleura is a subterclass of land and water-dwelling gastropods. The group consists of over 27,000 various species, among which are various groups of snails, slugs, and sea hares living across various diverse habitats around the world. It un ...

*** Euopistobranchia ***

Panpulmonata Panpulmonata is a taxonomic clade of snails and slugs in the clade Heterobranchia within the clade Euthyneura. Panpulmonata was established as a new taxon by Jörger et al. in October 2010. The older name "Pulmonata" referred to a group of euth ...

Older taxonomy

The families currently included in Heterobranchia have historically been placed in many different parts of the taxonomic class of gastropods. Earlier authors (such as J.E. Gray, 1840) considered Heterobranchia to consist of only marine gastropods, and conceptualized it as a borderline category, intermediate between the Opisthobranchia & Pulmonata, and all the other gastropods. The (sometimes recognized) category Heterostropha within the Heterobranchia, which includes such families as Architectonicidae, the sundial or staircase snails, is primarily characterized by a shell which has a heterostrophic protoconch, in other words the apical whorls are coiled in the opposite plane to the adult whorls. The classification of this group was revised by Ponder & Warén in 1988. According to the older taxonomy of the Gastropoda (Ponder & Lindberg, 1997) the Heterobranchia were ranked as a superorder.

2005 taxonomy

Heterobranchia is currently one of the main clades of gastropods. For a detailed taxonomy, see Taxonomy of the Gastropoda (Bouchet & Rocroi, 2005)#Clade Heterobranchia.

2010 taxonomy

Jörger et al. (2010) have redefined major groups within the Heterobranchia: they created the new clades

Euopisthobranchia Euopisthobranchia is a taxonomic clade of snails and slugs in the clade Heterobranchia within the clade Euthyneura. This clade was established as a new taxon by Jörger et al. in October 2010. Euopisthobranchia is a monophyletic portion of the ...

and

. A

cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

showing phylogenic relations of Heterobranchia as proposed by Jörger et al. (2010):