''Pyganodon grandis'', the giant floater, 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 ...

freshwater mussel Freshwater bivalves are one kind of freshwater mollusc, along with freshwater snails. They are bivalves that live in fresh water as opposed to salt water, which is the main habitat type for bivalves. The majority of species of bivalve molluscs ...

, an aquatic bivalve

mollusk Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is e ...

in the family

Unionidae The Unionidae are a family of freshwater mussels, the largest in the order Unionida, the bivalve molluscs sometimes known as river mussels, or simply as unionids. The range of distribution for this family is world-wide. It is at its most divers ...

, the river mussels. This species is fast-growing, large, and has a short lifespan. This species is 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 territori ...

and southeastern

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...

. Original description (Say 1829): "Shell very large, subovate; disk unequally wrinkled and undulated transversely, dark yellowish brown; umbo elevated; beak slightly elevated, with generally, two or three small sinuous, acute undulations; hinge margin slightly arquated, sometimes nearly rectilinear, somewhat angulated at its anterior termination, thence the edge descends by a nearly rectilinear, or slightly concave line to the anterior margin, which is considerably narrowed; sinus of the hinge margin concave; posterior margin widely rounded; within white margined, particularly before, with dusky."

References

* Binney, W.G. 1858. The complete writings of Thomas Say on the conchology of the United States. Bailliere Publ. NY * Haag, W. R. (2012). ''North American Freshwater Mussels: Natural History, Ecology, and Conservation''. Cambridge University Press. * Say, T. 1829. Descriptions of some new terrestrial and fluviatile shells of North America. New Harmony Disseminator of Useful Knowledge, New Harmony, Indiana. (see the description also in Binney's summary of Say's writing, 1858). Molluscs of Canada Molluscs of the United States

grandis Grandis may refer to: * Grandis (company), a company producing magnetoresistive random-access memory * Grandis (company), a company producing High quality Italian racing bicycles * Grandis (surname) * Mitsubishi Grandis The is a seven-seat ...

Bivalves described in 1829 {{Unionidae-stub