Physella is a genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of small, left-handed or sinistral, air-breathing freshwater snails, aquatic

Aquatic animal

An aquatic animal is an animal, either vertebrate or invertebrate, which lives in water for most or all of its life. It may breathe air or extract its oxygen from that dissolved in water through specialised organs called gills, or directly through its skin. Natural environments and the animals that...

 pulmonate gastropod mollusks in the family Physidae.

These snails eat algae, diatoms and other detritus.

Shell description

Snails in the family Physidae

Physidae

Physidae, common name bladder snails, are a monophyletic taxonomic family of small freshwater snails, aquatic pulmonate gastropod molluscs in the clade Hygrophila....

 have shells that are sinistral, which means that if you hold the shell such that the spire is pointing up, then the aperture is on the left-hand side.

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

Species

Species in the genus include:

• Physella acuta
  Physella acuta
  Physella acuta, common name the European physa, is a species of small, left-handed or sinistral, air-breathing freshwater snail, an aquatic gastropod mollusk in the family Physidae.-Shell description:...
  
  (Draparnaud, 1805) - Pewter Physa, type species, synonyms: Physella heterostropha (Say, 1817), Physella integra (Haldeman, 1841)
• Physella ancillaria (Say, 1825)
• Physella bermudezi (Aguayo, 1935) - Lowdome Physa
• Physella bottimeri (Clench, 1924) - Comanche Physa
• Physella boucardi (Crosse & P. Fischer, 1881) - Desert Physa
• Physella columbiana (Hemphill, 1890) - Rotund Physa
• Physella conoidea (P. Fischer & Crosse, 1886) - Texas Physa
• Physella cooperi (Tryon, 1865) - Olive Physa
• Physella costata (Newcomb, 1861) - Ornate Physa
• Physella cubensis (Pfeiffer, 1839)
• Physella globosa (Haldeman, 1841) - Globose Physa
• Physella gyrina
  Physella gyrina
  Physella gyrina common name the "tadpole physa", is a species of small, left-handed or sinistral, air-breathing freshwater snail, an aquatic pulmonate gastropod mollusk in the family Physidae.-Shell description:...
  
  (Say, 1821)
• Physella hendersoni (Clench, 1925)
• Physella hordacea (I. Lea, 1864) - Grain Physa
• Physella humerosa (Gould, 1855) - Corkscrew Physa
• Physella johnsoni (Clench, 1926) - Banff Springs Snail
• Physella lordi (Baird, 1863) - Twisted Physa
• Physella magnalacustris (Walker, 1901)
• Physella mexicana (Philippi, 1841) - Polished Physa
• Physella microstriata (Chamberlin & E. G. Berry, 1930)
• Physella natricina Taylor, 1988
• Physella osculans (Haldeman, 1841) - Cayuse Physa
• Physella parkeri
  Physella parkeri
  Physella parkeri is a species of small air-breathing freshwater snail, an aquatic gastropod mollusk in the family Physidae.Like others in the family, this species is sinistral or left-handed.- Distribution :...
  
  (Currier, 1881) - Broadshoulder Physa
• Physella propinqua (Tryon, 1865) - Rocky Mountain Physa
• Physella sayi
• Physella spelunca (Turner & Clench, 1974)
• Physella squalida (Morelet, 1851) - Squalid Physa
• Physella traski (I. Lea, 1864) - Sculpted Physa
• Physella utahensis (Clench, 1925)
• Physella vinosa (Gould, 1847) - Banded Physa
• Physella virgata (Gould, 1855)
• Physella virginea (Gould, 1847) - Sunset Physa
• Physella winnipegensis ..., 2004
• Physella wrighti
  Physella wrighti
  Physella wrighti, the Hotwater Physa, is a species of a freshwater snail, a gastropod in the Physidae family.- Distribution :It lives in British Columbia in Canada and it is endangered species there. The Canadian Species at Risk Act listed it in the List of Wildlife Species at Risk as being...
  
  Te & Clarke, 1985
• Physella zionis (Pilsbry, 1926)