Respiration
Since snails in the genus Helix are terrestrial rather than fresh-water or marine, they have developed a simple lung for respiration. (Most other snails and gastropods have gills,instead.)
Oxygen is carried by the blood pigment hemocyanin. Both oxygen and carbon dioxide diffuse in and out of blood through the capillaries. A muscular valve regulates the process of opening and closing the entrance of the lung. When the valve opens, the air can either leave or come into the lung. The valve plays an important role in reducing water loss and preventing drowning.
Read more about this topic: Helix (gastropod)