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Text: Eisenhour, David J, Helen I'Anson, Jr., Susan L. Keen, Allan Larson, Larry S Roberts, and Cleveland P Hickman. Integrated Principles of Zoology. 14 ed. New York: McGraw-Hill Science/Engineering/Math, 2007. Print.

Additional Online Sources:

http://en.wikipedia.org/wiki/Gastropod#Excretory_system