THE XERCES SOCIETY FOR INVERTEBRATE CONSERVATION

Aquatic Invertebrates in Pacific Northwest Freshwater Wetlands
An Identification Guide and Educational Resource

Planorbids are pulmonate (lunged) snails that live on a variety of substrates and eat algae. They are fairly tolerant of disturbance, and are most commonly collected in slow or still waters. Several genera may be found in the Northwest, although they can be difficult to distinguish when they are small, and they are often damaged during sampling or processing.

Among the Northwest genera are the very similar Gyraulus and Menetus, which can often be found together, and the larger and more distinctive Helisoma. These have all been collected in wetlands in the Willamette Valley in Oregon. These genera all share the characteristic flattened, disk-like shell of the family, and have no operculum protecting the soft body when withdrawn into the shell.

Size: small to xlarge
Identifying feature(s): no operculum; coil of the shell is completely or mostly flattened laterally
Habitat: most commonly in slow or still waters
Tolerance: tolerant and sediment tolerant