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.
John B. Burch (photographer; copyright holder), Mollusk Division, Museum of Zoology, University of Michigan-Ann Arbor
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