''Epioblasma stewardsonii'', the Cumberland leafshell or Steward's pearly mussel, is an extinct

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of freshwater mussel in the family Unionidae. This species was

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

to the drainages of the

Cumberland River The Cumberland River is a major waterway of the Southern United States. The U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map, accessed June 8, 2011 river drains almost of southern Kentucky and ...

and the

Tennessee River The Tennessee River is the largest tributary of the Ohio River. It is approximately long and is located in the southeastern United States in the Tennessee Valley. The river was once popularly known as the Cherokee River, among other names, ...

in the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

. Its natural

habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...

was riffle areas in large to medium size

river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...

s. Like most other members of this sensitive genus, it became extinct due

habitat destruction Habitat destruction (also termed habitat loss and habitat reduction) is the process by which a natural habitat becomes incapable of supporting its native species. The organisms that previously inhabited the site are displaced or dead, thereby ...

and pollution. The last documented occurrence of this species was in 1909. It appears to be most closely related to ''

Epioblasma flexuosa ''Epioblasma flexuosa'', the arcuate pearly mussel or leafshell, was a species of freshwater mussel, an aquatic bivalve mollusk in the family Unionidae, the river mussels. This species was endemic to the United States, where it was found in the ...

'', which is also now extinct.

References

Extinct bivalves stewardsonii Bivalves described in 1852 Taxonomy articles created by Polbot {{Unionidae-stub