Gastropoda

The gastropods are the largest and most succesful class of molluscs, with over 35000 species, comprising the snails and slugs. They typically have a well-defined head with two or four sensory tentacles, and a ventral foot, which gives them their name (Greek gaster, stomach, and poda, feet). They are distinguished by torsion, a process where the body coils to one side during development. Most members have a shell, which is in one piece and typically coiled or spiralled. In some members, the slugs, the shell is reduced or absent, and the body is streamlined so its torsion is relatively inconspicuous.