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Prosobranchia
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<p>Prosobranchia was a large <a href="/facts/Taxonomy_(biology)/Qkg8wuyw">taxonomic</a> <a href="/facts/Class_(biology)/a7MrgFu3">subclass</a> of sea snails, land snails and freshwater snails. This taxon of <a href="/facts/Gastropod/rYPqm3PT">gastropods</a> dates back to the 1920s. It has however been proven to be <a href="/facts/Polyphyly/o7lxKY74">polyphyletic</a> (consisting of more than one <a href="/facts/Lineage_(evolution)/wIChE4CL">lineage</a> of descent). Generally speaking in biology <a href="/facts/Taxonomy_(biology)/Qkg8wuyw">taxonomy</a> is required to reflect <a href="/facts/Phylogeny/f5vVEpeY">phylogeny</a>, 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. </p><p>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. </p><p><i>Prosobranch</i> means <i><a href="/facts/Gill/FWgM3Jp8">gills</a> in front</i> (of the <a href="/facts/Heart/fF4KSGdk">heart</a>). In contrast <i><a href="/facts/Opisthobranchia/C4K6BhwU">opisthobranch</a></i> means <i>gills behind</i> (and to the right of the heart). Prosobranchs have their gills, <a href="/facts/Mantle_(mollusc)/GqSY3XB6">mantle</a> cavity and <a href="/facts/Anus/KoCBptr5">anus</a> situated in front of their heart. Most prosobranchs have separate sexes. </p><p>The majority of <a href="/facts/Marine_(ocean)/8W8lYgjD">marine</a> <a href="/facts/Gastropoda/rYPqm3PT">gastropods</a> are prosobranch, as are a few land snails and freshwater snails. The prosobranch gastropods include the majority of marine snails, among them <a href="/facts/Conch/Ie4rhJQx">conches</a>, <a href="/facts/Conus/2s30wDxM">cones</a>, <a href="/facts/Cowry/RDoCfldh">cowries</a>, <a href="/facts/Limpet/cAyIMhoT">limpets</a>, <a href="/facts/Murex/UX1nJBU1">murexes</a>, <a href="/facts/Periwinkle_(mollusc)/WhbdquHy">periwinkles</a>, <a href="/facts/Volutidae/2E8F3DT0">volutes</a> and <a href="/facts/Whelk/zeyfvQ1X">whelks</a>, as well as numerous freshwater groups, and some land snails with an <a href="/facts/Operculum_(gastropod)/dAluNWBS">operculum</a>. </p>