Seasnails (Prosobranchia)

Most seashells that people find on the beach belong to the Caenogastropoda. Although most of the group are marine, many are also found in freshwater or even on land (terrestrial). All caenogastropods have a coiled shell (at least in the larval stage) with an opening which can be closed by an operculum in most species. The soft body has a head complete with two eyes located on the tops of two tentacles, and a large flat foot, which is used for locomotion. 

Some of the families in this group include: whelks (Buccinidae), periwinkles (Littorinidae), cones (Conidae), murex shells (Muricidae) and volutes (Volutidae).