But in order for gas exchange to occur, access to the respiratory organs must occur through an opening within the mantle. This opening, called a pneumostome, can be seen in the inset box at the bottom of this image. Next time you see a land snail or a slug, look for the pneumosome. It can open and close, but with a little patience you will see this most wonderful adaptation for terrestrial gastropods.

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The Respiratory System
The body of a terrestrial gastropod (land snails and slugs) is surrounded by a blanket of tissue call the mantle, and between the body organs (viseral mass) and the mantle is space called the mantle cavity. It is within the mantle cavity where significant gas exchange occurs.