''Rotundaria houstonensis'', the smooth pimpleback, is a

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 native to 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 ...

. It is endemic to the

Colorado Colorado (, other variants) is a state in the Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of t ...

and

Brazos River The Brazos River ( , ), called the ''Río de los Brazos de Dios'' (translated as "The River of the Arms of God") by early Spanish explorers, is the 11th-longest river in the United States at from its headwater source at the head of Blackwater Dr ...

drainages in

Texas Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...

. This species has experienced a decline due to pollution and habitat loss. In 2011 the

United States Fish and Wildlife Service The United States Fish and Wildlife Service (USFWS or FWS) is an agency within the United States Department of the Interior dedicated to the management of fish, wildlife, and natural habitats. The mission of the agency is "working with othe ...

determined that although this species met the criteria for listing under the

Endangered Species Act The Endangered Species Act of 1973 (ESA or "The Act"; 16 U.S.C. § 1531 et seq.) is the primary law in the United States for protecting imperiled species. Designed to protect critically imperiled species from extinction as a "consequence of ec ...

, its listing should be precluded for higher-priority species. Its current legal status is "Candidate".NatureServe
/ref> It was formerly classified under ''

Quadrula ''Quadrula'' is a genus of freshwater mussels, aquatic bivalve mollusks in the family Unionidae native to rivers of the American Midwest and mid-south. All have thick nacreous shells with well-developed hinge teeth, many also with external she ...

'', but in 2012 it was moved to ''Rotundaria'' based on genetic evidence.

References

houstonensis Endemic fauna of the United States Natural history of Texas Bivalves described in 1859 Taxonomy articles created by Polbot {{Unionidae-stub