Re: How do gills work on a land snail?

Rachael,
The following has been paraphrased from a great source of information on 
invertebrates:  "Discoveries in Biology" by D.M. Ogilvie and R.H. Stinson 
(1992), Copp Clark Pitman Ltd., Toronto. 
Most snails are aquatic and use gills for respiration, but land snails like 
Cepaea (brown or white-lipped garden snail) are air-breathers, and thus a 
member of the subclass Pulmonata (which includes slugs). To breathe air 
Cepaea makes use of an organ like a lung. The snail has a moist surface 
enclosed within a chamber just under the top part of the shell behind the 
extended 'head and neck'. This is called a mantle cavity, which acts as a 
lung, and to regulate water loss. Air moves in and out of this chamber by 
passing through a small, muscular hole (called a pneumostome). This hole is 
only found in the terrestrial snails, and is visible under the upper side 
of the top lip of the shell. Air moving into the mantle cavity comes in 
contact with the branching pulmonary artery that reaches under the mantle 
cavity, and oxygen diffuses across the moist membranes and into the 
circulatory system. To find out more details (such as how carbon dioxide is 
removed across the snails permeable surfaces, information which I have not 
been able to uncover), you may want to start with a classic text "The Shell 
Makers, Introducing Molluscs" by A.Solem (1974), Wiley, New York (If it is 
available in Alaska!!)
Cheers,
Neala MacDonald