A Treatise on Limnology. IV, The Zoobenthos. Save Our Streams. Monitor's Guide to Aquatic Macroinvertebrates.
Snails possess a single shell that is usually coiled, although sometimes flattened and cone shaped.
Because prosobranchs depend on oxygen dissolved in the water for respiration, they are intolerant of sites where dissolved oxygen is scarce, such as sites of organic pollution. They also are absent from temporary waters. In many pulmonates the mantle cavity may be filled either with air or with water, so that the mantle wall can work either as a lung or as a gill. The general greater abundance of pulmonates in eutrophic water is probably connected with productive waters being more susceptible to high respiratory loss of oxygen and the resulting low oxygen concentrations in the water. No plate-like covering over the shell opening.