THE XERCES SOCIETY FOR INVERTEBRATE CONSERVATION

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

Physa is one snail that can be identified easily, because is it is the only "left-handed" or sinistral snail in the Northwest. This means that when the shell's apex is pointing up and the aperture is facing you, the opening is to your left. Physa is a tolerant snail that is collected with some regularity, though more in slower, lower elevation waters.

As with most other snails, Physa are algae scrapers. However, they are part of the group called pulmonates, which breathe air through a siphon (seen in the center photograph above) and don't have an operculum to protect their body when it is withdrawn into the shell. The body is occasionally visible through their shell, giving them a black and yellow-spotted appearance.

Size: large
Identifying feature(s): the shell coils to the left when the apex is pointed up and the aperture is facing you (sinistral); no operculum; coil of the shell is cone-like and bulging
Habitat: diverse fresh water
Tolerance: tolerant