A group of garden snails, Helix aspera, sheltering a flower pot in a garden in Norfolk UK. The pictures shows a snail moving across a mass of stationary snails. The hard shell of snails protects the soft tissue within it ( the mantle ). In this picture the foreground snail has its head extended, showing the tentacles bearing terminal eyes. As the picture shows, the shell of a snail is not bilaterally symmetrical. All snails in the Helicid family coil the same way, described as dextral or "right-handed". The shell is made from calcium carbonate, and can be repaired by the snail if it suffers small damage. The calcium carbonate is coated on the outside with a layer of organic material, the periostracum, which gives the snail its colour and pattern