Members of the freshwater pulmonate family Physidae possess a complex of muscles that is unique amongst gastropods. This complex was given the name "physid musculature". The physid musculature has two main components, the physid muscle sensu stricto and the fan muscle. The physid musculature is responsible for a unique ability of physids to rapidly flick their shells from side to side — a reaction that frequently enables them to escape predation.
These small snails, like all the species in the family Planorbidae, have shells that are sinistral, which means that when the shell is held with the spire pointing up and the aperture facing the viewer, then the aperture is on the left-hand side.
Species in the genus include:
- Physa ancillaria (Say, 1825) - Pumpkin Physa
- †Physa aridi Mezzalira, 1974 - fossil from Brazil
- Physa carolinae Johns Island, South Carolina 2010 by Amy Wethington in ditch, then confirmed at the University of Alabama
- Physa concolor
- Physa fontinalis - Fountain bladder snail - type species
- Physa hordacea (I. Lea, 1864)
- Physa jennessi Dall, 1919
- Physa lordi (Baird, 1863)
- Physa marmorata Guilding, 1828 - synonyms: Physa mosambiquensis Clessin, 1886 and Physa waterloti
- Physa megalochlamys Taylor, 1988
- †Physa mezzalirai Ghilardi, Carbonaro & Simone, 2011 - fossil from Brazil
- Physa natricina Taylor, 1988
- Physa nuttalli
- Physa propingua (Tryon, 1865)
- Physa pumilia Conrad, 1834
- Physa siberica Westerlund, 1876
- Physa skinneri Taylor, 1954
- Physa vernalis Taylor et Jokinen, 1984
- Physa sp., Lake Winnipeg Physa, lives in Manitoba in Canada. It was classified as endangered by COSEWIC. COSEWIC recommendation has been forwarded to the Minister of the Environment of Canada and a decision for listing at the List of Wildlife Species at Risk of the Canadian Species at Risk Act was pending in 2005.
- Physa acuta Draparnaud, 1805, Physa heterostropha (Say, 1817), Physa integra (Haldeman, 1841) and Physa natricina Taylor, 1988 are synonyms of Physella acuta (Draparnaud, 1805)
- Physa columbiana (Hemphill, 1890) is a synonym for Physella columbiana (Hemphill, 1890)
- Physa gyrina (Say, 1821) is a synonym for Physella gyrina (Say, 1821)
- Draparnaud J. P. R. (1801). Tableau des mollusques terrestres et fluviatiles de la France. - pp. [1-2], 1-116. Montpellier, Paris. (Renaud; Bossange, Masson & Besson).
- "Physella". NatureServe Explorer, accessed 9 April 2010.
- Simone, L.R.L. & Mezzalira, S. 1994. Fossil Molluscs of Brazil. Boletim do Instituto Geológico 11: 1–202.
- Appleton C. C. & Dana P. (2005). "Re-examination of Physa mosambiquensis Clessin, 1886 and its relationship with other Aplexinae (Pulmonata: Physidae) reported from Africa". African Invertebrates 46: 71-83. abstract
- Ghilardi,RP; Carbonaro, FA; & Simone, LRL. 2011. Physa mezzalirai, a new cretaceous basommatophoran from Adamantina formation, Brazil. Strombus 18(1-2): 1-14. http://www.conchasbrasil.org.br/strombus/online.asp
- COSEWIC. 2005. Canadian Species at Risk. Committee on the Status of Endangered Wildlife in Canada. 64 pp., page 13.
- Janus, Horst, 1965. ‘’The young specialist looks at land and freshwater molluscs’’, Burke, London