|MadSci Network: Zoology|
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
Try the links in the MadSci Library for more information on Zoology.