PROSOBRANCH

any snail of the subclass Prosobranchia, class Gastropoda. Most of these primitive snails are marine; a few live on land or in fresh water. Many prosobranchs breathe by means of gills, which are located in front of the heart; some have a special respiratory structure on the mantle or, in land species, a simple pulmonary cavity. The auricle of the heart is in front of the ventricle. Larval torsion results in a figure-eight arrangement of the viscera and nerve cord that persists throughout life. Most species have a lid (operculum) on the foot that closes the shell when the animal retracts. The sexes are separate. For further information on members of the prosobranch group, see abalone; conch; cone shell; cowrie; ear shell; freshwater snail; helmet shell; land snail; limpet; mitre shell; murex; olive shell; periwinkle; slipper shell; top shell; triton shell; turban shell; volute; wentletrap; whelk; worm shell.