Editing Prosobranchia

{{Short description|Historic group of molluscs}}
{{distinguish|text=the bivalve order [[Protobranchia]]}}
[[File:Haeckel Prosobranchia.jpg|thumb|Shells from a variety of prosobranch gastropods, from [[Ernst Haeckel]]'s ''[[Artforms of Nature]]'', 1904.]]
'''Prosobranchia''' was a large [[Taxonomy (biology)|taxonomic]] [[Class (biology)|subclass]] of sea snails, land snails and freshwater snails. This taxon of [[gastropod]]s dates back to the 1920s. It has however been proven to be [[polyphyly|polyphyletic]] (consisting of more than one [[lineage (evolution)|lineage]] of descent). Generally speaking in biology [[Taxonomy (biology)|taxonomy]] is required to reflect [[phylogeny]], in other words the classification of a group must reflect its evolutionary descent, as far as that is known, so the taxon Prosobranchia is no longer considered suitable to be used.

One can still encounter this subclass used as if it is still valid in many texts and websites. Although Prosobranchia is no longer generally accepted as a taxon by people who study living Mollusca, still the term '''prosobranch''' is legitimately used as an anatomically descriptive adjective or noun, and the taxon Prosobranchia is still sometimes used by paleontologists.

''Prosobranch'' means ''[[gill]]s in front'' (of the [[heart]]). In contrast ''[[opisthobranchia|opisthobranch]]'' means ''gills behind'' (and to the right of the heart). Prosobranchs have their gills, [[Mantle (mollusc)|mantle]] cavity and [[anus]] situated in front of their heart. Most prosobranchs have separate sexes.

The majority of [[Marine (ocean)|marine]] [[Gastropoda|gastropods]] are prosobranch, as are a few land snails and freshwater snails. The prosobranch gastropods include the majority of marine snails, among them [[conch]]es, [[conus|cones]], [[cowry|cowries]], [[limpet]]s, [[murex]]es, [[periwinkle (mollusc)|periwinkles]], [[volutidae|volute]]s and [[whelk]]s, as well as numerous freshwater groups, and some land snails with an [[Operculum (gastropod)|operculum]].

==Description==
[[File:Prosobranchia.gif|thumb|left|Three views of a [[gastropod shell|shell]] of a ''[[Harpa]]'' species, a prosobranch gastropod.]]
[[File:Naturalis Biodiversity Center - RMNH.MOL.129087 - Chicoreus ramosus (Linnaeus, 1758) - Muricidae - Mollusc shell.jpeg|thumb|left|''[[Chicoreus ramosus]]'', a prosobranch gastropod.]]
The majority of prosobranchs have an [[operculum (gastropod)|operculum]], a [[corneous]] or [[calcareous]] plate situated on the [[Dorsum (biology)|dorsal]] surface of the foot. In many prosobranchs, the animal can completely close the [[aperture (mollusc)|aperture]] with the operculum.

The nervous system of prosobranchs is twisted into a figure 8 due to a developmental process known as [[torsion (gastropod)|torsion]]. The eyes are situated at the base of the [[tentacle]]s.

==Taxonomic context==
The taxonomy of the gastropods is changing rapidly. The old classification ([[Johannes Thiele (zoologist)|Johannes Thiele]]) divided Gastropoda into three subclasses: Prosobranchia, [[Opisthobranchia]] and [[Pulmonata]]. The subclass Prosobranchia ([[Henri Milne-Edwards]]) was further divided into the orders [[Archaeogastropoda]], [[Mesogastropoda]] and [[Neogastropoda]]. The new version of the gastropod classification is explained in [[Taxonomy of the Gastropoda (Ponder & Lindberg, 1997)|'' Taxonomy of the Gastropoda'' (Ponder & Lindberg, 1997)]].

==References==
*Thiele, J., 1929–1935. ''Handbuch der Systematischen Weichtierkunde''. 2 vols. 1154 p., 584 figs.
*Bieler, R. & P. M. Mikkelsen (eds.), 1992. ''Handbook of Systematic Malacology, Part 1 (Loricata [Polyplacophora]; Gastropoda: Prosobranchia)''.  [[Smithsonian Institution]] and [[National Science Foundation]], xviii + 625 pp., 470+1 text-fig. (Annotated English-language edition of: Thiele, J., ''Handbuch der systematischen Weichtierkunde'', Teil 1). Also published, in 1993, by Gustav Fischer Verlag, Stuttgart/Jena/New York.
*{{Cite journal | doi = 10.1146/annurev.es.23.110192.001523 | last1 = Bieler | first1 = R. | year = 1992 | title = Gastropod phylogeny and systematics | journal = Annual Review of Ecology and Systematics | volume = 23 | issue = 1 | pages = 311–338 | bibcode = 1992AnRES..23..311B }}
*{{Cite journal | doi = 10.1093/mollus/54.4.367 | last1 = Haszprunar | first1 = G. | year = 1988 | title = On the origin and evolution of major gastropod groups, with special reference to the Streptoneura | journal = [[Journal of Molluscan Studies]] | volume = 54 | issue = 4| pages = 367–441 }}
* {{Cite journal | last1 = Bieler | first1 = R. | year = 1990 | title = Haszprunar's "clado-evolutionary" classification of the Gastropoda - a critique | journal = [[Malacologia]] | volume = 31 | issue = 2| pages = 371–380 }}

{{Authority control}}

[[Category:Obsolete gastropod taxa]]
[[Category:Gastropod taxonomy]]
[[Category:Mollusc subclasses]]