Heterobranchia

Heterobranchia, the heterobranchs (meaning "different gill"), is a taxonomic clade of snails and slugs, which includes marine, aquatic, and terrestrial gastropod molluscs.

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.

Taxonomy

Current taxonomy

Source:

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

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 and Panpulmonata.

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

Further reading

• Dinapoli A. (2009). Phylogeny and Evolution of the Heterobranchia (Mollusca, Gastropoda). Thesis, Frankfurt am Main, 176 pp. [permanent dead link].
• Dinapoli A.; Klussmann-Kolb A. (2010). "The long way to diversity – Phylogeny and evolution of the Heterobranchia (Mollusca: Gastropoda)"". Molecular Phylogenetics and Evolution. 55 (1): 60–76. Bibcode:. doi:. PMID .