page_title: Prosobranchia
section_title: Description
hierarchical_section_title: Prosobranchia / Description
caption_attribution_description: Chicoreus ramosus (Linnaeus, 1758)
context_page_description: 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. 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.
  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. In contrast opisthobranch means gills behind. 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.
context_section_description: 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.
caption: Chicoreus ramosus, a prosobranch gastropod.
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