Eleven aquatic and 26 terrestrial species of mollusks have been identified in and around Grand Canyon National Park. Of the aquatic species, two are bivalves (clams) and nine are gastropods (snails). All of the aquatic snails located in Grand Canyon are of the subclass Pulmonata. This means that although they are aquatic, they are lung breathers. They do not have gills, but have a large pulmonary sac which they use for gaseous exchange. Three of the nine snail species found here are lymnaeids of the genus Fossaria. Lymnaeid snails have shells that coil to the right. Physids, of which Grand Canyon has five species of the genus Physella, are snails that possess shells that coil to the left. The remaining aquatic snail species is called a planorbid of the genus Gyralus. Planorbid snail shells are coiled in a single plane, appearing flatter than most snails.
The two aquatic bivalves are thought to be introduced species, since they were found in a cobble bar near Lees Ferry just downriver from the Glen Canyon Dam. These two clam species are of the genus Pisidium.
Twenty-six species of terrestrial gastropods have been identified, primarily land snails and slugs. The ambersnail family, Succineidae, is of special interest in Grand Canyon. This family of land snails gets its common name, "amber snail," from the snails' characteristic orange colored shell. One species of amber snail found in the park, the Kanab Ambersnail (Oxyloma haydeni kanabensis), is listed as endangered by the U.S. Fish and Wildlife Service. Only two populations of this species are known to exist.