Identification
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Caption
Gyraulus.The Planorbidae is a freshwater snail family of the subclass Pulmonata. These snails, although aquatic, are lung breathers. Gills are lacking; instead there is a large pulmonary sac for gaseous exchange. In the snail shown here, nearly half of the last whorl is occupied by the lung, clearly visible as an air-filled space. The Planorbidae are coiled in one plane, i.e., they are planate, a characteristic from which the family name is derived.
Dr. John B. Burch, Ph.D. 
(photographer, copyright holder), Mollusk Division, Museum of Zoology, University of Michigan
