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A live individual of Physa marmorata

Physa is a genus of small, left-handed or sinistral, air-breathing freshwater snails, aquatic pulmonate gastropod mollusks in the family Physidae.

These snails eat algae, diatoms and detritus.


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.

Shell description[edit]

These small snails, like all the species in the family Physidae, 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.

The shells of Physa species have a long and large aperture, a pointed spire, and no operculum. The shells are thin and corneous, and rather transparent.


Species in the genus include:


  • 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)


  1. ^ 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).
  2. ^ "Physella". NatureServe Explorer, accessed 9 April 2010.
  3. ^ Simone L. R. L. & Mezzalira S. (1994). "Fossil Molluscs of Brazil". Boletim do Instituto Geológico 11: 1–202.
  4. ^ Wethington A. R., Wise J. & Dillon R. T. (2009). "Genetic and morphological characterization of the Physidae of South Carolina (Pulmonata: Basommatophora), with description of a new species". The Nautilus 123: 282-292. PDF.
  5. ^ a b 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
  6. ^ Ghilardi R. P., Carbonaro F. A. & Simone L. R. L. (2011). "Physa mezzalirai, a new cretaceous basommatophoran from Adamantina formation, Brazil". Strombus 18(1-2): 1-14. abstract.
  7. ^ 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


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