Heterobranchia

Taxobox
name = Heterobranchia


image_caption = The sea butterfly or pteropod gastropod, "Clione limacina"
regnum = Animalia
phylum = Mollusca
classis = Gastropoda
subclassis = Orthogastropoda
superordo = Heterobranchia
subdivision_ranks = Orders
subdivision =
Heterostropha

Opisthobranchia

Pulmonata

Heterobranchia, the "heterobranchs", (meaning "different-gilled snails"), is a taxonomic superorder of sea snails, marine gastropod mollusks.

(Note: Gastropod taxonomy has been in flux for many years, and this is especially true currently, because of new research in molecular phylogeny. Because of all this on-going change, different reliable sources can yield very different classifications. This is especially true within groups which are poorly understood in general.)

This superorder contains a diverse and interesting group of families. The similarity in the structure of the gills within this group makes the various families eligible for membership, despite all the other differences they show.

The families included in this recently established superorder of mollusks [cite journal | quotes=no | author = Haszprunar G. |title = The Heterobranchia ― a new concept of the phylogeny of the higher Gastropoda|year = 1985| journal = Zeitschrift für zoologische Systematik und Evolutionsforschung|volume = 23| issue = 1 | pages = 15–37 ISSN 0044-3808] have historically been placed in many different parts of the taxonomic class of gastropods. Earlier authors (as J.E. Gray, 1840) placed the Heterobranchia as a borderline category intermediate between the Opisthobranchia & Pulmonata, and all the other gastropods.

The (sometimes recognized) order 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 has been revised by Ponder & Warén (1988) [cite journal | quotes=no | author = Ponder, W. F. & Warén, A. |title = Classification of the Caenogastropoda and Heterostropha- A list of family-group names and higher taxa|year = 1988| journal = Malacological review supplement |volume = 4| issue =| pages = 288–317] .

(In contrast to the heterobranchs, the bodies of the Opisthobranchia have undergone detorsion (unwinding). They have essentially evolved back to the bilateral symmetry of their ancestors. The mantle cavity of the Pulmonata has modified into an air-breathing organ. They are also characterized by detorsion and a symmetrically-arranged nervous system. The pulmonates usually lack an operculum and are hermaphroditic. The order Pulmonata contains most land snails and slugs, many freshwater snails, and a small number of fully marine species.)

Taxonomy of the Heterobranchia

Superorder Heterobranchia J.E. Gray, 1840
*Order Heterostropha P. Fischer, 1885 (sometimes Allogastropoda Haszprunar, 1985) (paraphyletic)
*Order Opisthobranchia Milne-Edwards, 1848 (paraphyletic)
**Suborder Cephalaspidea P. Fischer, 1883 (headshield slugs)
**Suborder Sacoglossa Von Ihering, 1876 (sap-suckling slugs)
**Suborder Anaspidea P. Fischer, 1883 (sea hares)
**Suborder Notaspidea P. Fischer, 1883 (sidegill slugs)
**Suborder Thecosomata de Blainville, 1824 (sea butterflies)
***Infraorder Euthecosomata
***Infraorder Pseudothecosomata
**Suborder Gymnosomata de Blainville, 1824 (sea angels)
**Suborder Nudibranchia de Blainville, 1814 (nudibranchs, true sea slugs))
***Infraorder Anthobranchia Férussac, 1819
***Infraorder Cladobranchia Willan & Morton, 1984
*Order Pulmonata Cuvier in Blainville, 1814 (pulmonates)
**Suborder Systellommatophora Pilsbry, 1948
**Suborder Basommatophora Keferstein in Bronn, 1864 (freshwater pulmonates, pond snails)
**Suborder Eupulmonata Haszprunar & Huber, 1990
***Infraorder Acteophila (Dall, 1885 (formerly Archaeopulmonata)
***Infraorder Trimusculiformes Minichev & Starobogatov, 1975
***Infraorder Stylommatophora A. Schmidt, 1856 (land snails)
****Subinfraorder Orthurethra
****Subinfraorder Sigmurethra

New studies, published in 2004, cite journal | author=Cristina Grande, José Templado, J. Lucas Cervera and Rafael Zardoya| title=Molecular Phylogeny of Euthyneura (Mollusca: Gastropoda) (full text on line)| journal=Mol. Biol. Evol. | year=2004| volume=21| issue=2| url=http://mbe.oxfordjournals.org/cgi/content/full/21/2/303| pages=303–313| pmid=14660702| doi=10.1093/molbev/msh016] put the monophyletic Pulmonata and the paraphyletic Opisthobranchia together in the clade Euthyneura Spengel 1881.. This clade together with the paraphyletic group Heterostropha (pyramidelids and other related groups) define the clade Heterobranchia.

Clade Heterobranchia
*Grade Heterostropha
*Clade Euthyneura
**Grade Opisthobranchia
**Clade Pulmonata

References