Clams that move do so by projecting a “foot,” which is a muscular, fleshy organ that can easily be projected from between the clams' two shells. Physically speaking, however, clams have no legs, arms, mouths or heads.
The shells of clams are opened via two strong muscles and are needed because clams themselves have soft bodies. Despite not having legs or arms, clams still have hearts and blood vessels. Clams also have gills, which are used for removing not only oxygen but also food particles from water. This is why clams don't require mouths to eat.
The foot is not the only thing that clams extend out past their shells. To both breathe and feed, clams have to stick the ends of their siphons outside of their shells. Food is drawn into the clams' bodies by using cilia, which stir up water and make small currents. At this point, the food is passed throughout the clams' digestive systems, and the excess water is forced back out through the siphons.
Both little-neck and hard-shell clams are often referred to as quahogs. This was a name given to them by the Narraganset Indians. They are traditionally found along the Gulf of Mexico and on the Atlantic coast.