Any of a large phylum (Mollusca) of invertebrate animals (as snails, clams, or squids) with a soft unsegmented body usually enclosed in a calcareous shell. Often occurring in calcareous deposits, they may give useful information if associated with archaeological remains. A group may give an indication of environmental conditions and general climatic conditions. More tentatively, a deposit containing mollusks may be dated against the geological scale. The phylum Mollusca is divided into five classes: Amphineura (chitons), Gastropoda (snails and slugs), Scaphopoda (elephant's tusk shells), Lamellibranchiata (bivalve mollusks, such as mussels, clams, oysters), and Cephalopoda (octopus and squids). With the exception of the gastropods, most of these groups are aquatic; shells of gastropods and lamellibranchs are frequently found on archaeological sites. Shells also remain from the exploitation of these animals for food, most often found in middens found near coastal sites. Land snails are increasingly used as an adjunct to pollen and insect analysis in attempts to reconstruct past environments.