In addition to the hard calcareous shell that covers and protects the internal organs, the head and foot region can be observed when the snails are fully extended. When they are active, the organs such as the lung, heart, kidney and intestines remain inside the shell; only the head and foot emerge.
The head of the snail has two pairs of tentacles: the upper and larger pair contains the eyes, and the lower pair are used to feel the ground in front. The mouth is located just underneath the head. The tentacles can be withdrawn or extended depending on the situation. The mouth has a unique tongue called a “radula” that is composed of many fine chitinous teeth. This serves for rasping and cutting food.
[Text with great thanks from English Wikipedia – Species Pages, Genus Helix Linnaeus]