Prosobranchia

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Shells from a variety of prosobranch gastropods, from Ernst Haeckel's Artforms of Nature, 1904. Haeckel Prosobranchia.jpg
Shells from a variety of prosobranch gastropods, from Ernst Haeckel's Artforms of Nature , 1904.

Prosobranchia was a large taxonomic subclass of sea snails, land snails and freshwater snails. This taxon of gastropods dates back to the 1920s. It has however been proven to be polyphyletic (consisting of more than one lineage of descent). Generally speaking in 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.

Contents

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 gills in front (of the heart). In contrast opisthobranch means gills behind (and to the right of the heart). Prosobranchs have their gills, mantle cavity and anus situated in front of their heart. Most prosobranchs have separate sexes.

The majority of marine gastropods are prosobranch, as are a few land snails and freshwater snails. The prosobranch gastropods include the majority of marine snails, among them conches, cones, cowries, limpets, murexes, periwinkles, volutes and whelks, as well as numerous freshwater groups, and some land snails with an operculum.

Description

Three views of a shell of a Harpa species, a prosobranch gastropod. Prosobranchia.gif
Three views of a shell of a Harpa species, a prosobranch gastropod.
Chicoreus ramosus, a prosobranch gastropod. Naturalis Biodiversity Center - RMNH.MOL.129087 - Chicoreus ramosus (Linnaeus, 1758) - Muricidae - Mollusc shell.jpeg
Chicoreus ramosus, a prosobranch gastropod.

The majority of prosobranchs have an operculum, a corneous or calcareous plate situated on the dorsal surface of the foot. In many prosobranchs, the animal can completely close the aperture with the operculum.

The nervous system of prosobranchs is twisted into a figure 8 due to a developmental process known as torsion. The eyes are situated at the base of the tentacles.

Taxonomic context

The taxonomy of the gastropods is changing rapidly. The old classification (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).

Related Research Articles

<span class="mw-page-title-main">Gastropoda</span> Class of molluscs

Gastropods, commonly known as slugs and snails, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda.

<span class="mw-page-title-main">Opisthobranchia</span> Informal group of gastropods

Opisthobranchs is a now informal name for a large and diverse group of specialized complex gastropods which used to be united in the subclass Opisthobranchia. That taxon is no longer considered to represent a monophyletic grouping.

<span class="mw-page-title-main">Archaeogastropoda</span> Order of gastropods

Archaeogastropoda was a taxonomic order of sea snails used in older classifications of gastropods, i.e. snails and slugs. Archeogastropoda are marine prosobranch gastropod mollusks, mainly herbivores, typically having two gills and a double-chambered heart, with the eggs and sperm discharged directly into the water. They were traditionally regarded as a relatively primitive group.

<span class="mw-page-title-main">Johannes Thiele (zoologist)</span> German zoologist

Karl Hermann Johannes Thiele was a German zoologist specialized in malacology. Thiele was born in Goldap, East Prussia. His Handbuch der systematischen Weichtierkunde is a standard work. From 1904 until his retirement in 1925 he was the curator of the malacological collection at the Museum für Naturkunde in Berlin. Thiele described more than 1.500 new species of molluscs; until today their types are deposited with the Museum of Natural History in Berlin. Especially important are his works on the Mollusca of the First German Antarctica Expedition and of the German Deep Sea Expedition aboard the vessel Valdivia.

<span class="mw-page-title-main">Mesogastropoda</span> Historic group of snails

Mesogastropoda was for many years a traditional taxonomic group of snails, an order. The order was composed mostly of sea snails, but it also included some land snails and freshwater snails, all of which were prosobranch gastropod mollusks.

<span class="mw-page-title-main">Neogastropoda</span> Clade of sea snails

Neogastropoda is an order of sea snails, both freshwater and marine gastropod molluscs.

<span class="mw-page-title-main">Heterobranchia</span> Clade of gastropods

Heterobranchia, the heterobranchs, is a taxonomic clade of snails and slugs, which includes marine, aquatic and terrestrial gastropod mollusks.

<span class="mw-page-title-main">Cephalaspidea</span> Order of gastropods

The order Cephalaspidea, also known as the headshield slugs and bubble snails, is a major taxon of sea slugs and bubble snails, marine gastropod mollusks within the larger clade Euopisthobranchia. Bubble shells is another common name for these families of marine gastropods, some of which have thin bubble-like shells. This clade contains more than 600 species.

<span class="mw-page-title-main">Pulmonata</span> Informal group of gastropods

Pulmonata or pulmonates, is an informal group of snails and slugs characterized by the ability to breathe air, by virtue of having a pallial lung instead of a gill, or gills. The group includes many land and freshwater families, and several marine families.

<span class="mw-page-title-main">Caenogastropoda</span> Clade of sea snails

Caenogastropoda is a taxonomic subclass of molluscs in the class Gastropoda. It is a large diverse group which are mostly sea snails and other marine gastropod mollusks, but also includes some freshwater snails and some land snails. The subclass is the most diverse and ecologically successful of the gastropods.

<span class="mw-page-title-main">Littorinimorpha</span> Order of gastropods

Littorinimorpha is a large order of snails, gastropods, consisting primarily of sea snails, but also including some freshwater snails and land snails.

<span class="mw-page-title-main">Basommatophora</span> Informal group of gastropods

Basommatophora was a term that was previously used as a taxonomic informal group, a group of snails within the informal group Pulmonata, the air-breathing slugs and snails. According to the taxonomy of the Gastropoda, whenever monophyly has not been tested, or where a traditional taxon of gastropods has now been discovered to be paraphyletic or polyphyletic, the term "group" or "informal group" was used.

<span class="mw-page-title-main">Thiaridae</span> Family of gastropods

Thiaridae, common name thiarids or trumpet snails, is a family of tropical freshwater snails with an operculum, aquatic gastropod mollusks in the superfamily Cerithioidea.

<span class="mw-page-title-main">Megalomastomatidae</span> Family of gastropods

Megalomastomatidae is a family of tropical land snails with an operculum, terrestrial gastropod mollusks in the superfamily Cyclophoroidea.

<span class="mw-page-title-main">Lithoglyphidae</span> Family of gastropods

Lithoglyphidae is a family of small freshwater snails with gills and an operculum, aquatic gastropod mollusks.

The taxonomy of the Gastropoda, as revised by Winston Ponder and David R. Lindberg in 1997, is an older taxonomy of the class Gastropoda, the class of molluscs consisting of all snails and slugs. The full name of the work in which this taxonomy was published is Towards a phylogeny of gastropod molluscs: an analysis using morphological characters.

<span class="mw-page-title-main">Vetigastropoda</span> Clade of sea snails

Vetigastropoda is a major taxonomic group of sea snails, marine gastropod mollusks that form a very ancient lineage. Taxonomically the Vetigastropoda are sometimes treated as an order, although they are treated as an unranked clade in Bouchet and Rocroi, 2005.

<span class="mw-page-title-main">Seguenzioidea</span> Superfamily of gastropods

Seguenzioidea is a superfamily of minute to medium-sized sea snails, marine gastropod mollusks in the clade Vetigastropoda.

<i>Cylindrobulla</i> Genus of gastropods

Cylindrobulla is a genus of sea snails or bubble snails, marine gastropod mollusks in the clade Sacoglossa.

Haedropleura laeta is a species of sea snail, a marine gastropod mollusk in the family Horaiclavidae.

References