Heterobranchia, the heterobranchs (meaning "different gill"), is a taxonomic clade of and , which includes marine, Aquatic animal, and terrestrial gastropod .
Heterobranchia is one of the main clades of gastropods. Currently Heterobranchia comprises two groups: the Opisthobranchia, and the Pulmonata.
Diversity
The two subdivisions of this large clade are quite diverse:
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Opisthobranchia are virtually all marine species, some gastropod shell and some not, and comprise about 25 families and 2000 species of the Cephalaspidea, the Sea slug, as well as the Aplysiida.
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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
Heterobranchia
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 Winston 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
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Dinapoli A. (2009). Phylogeny and Evolution of the Heterobranchia (Mollusca, Gastropoda). Thesis, Frankfurt am Main, 176 pp. PDF.
