''Epioblasma haysiana'', the acornshell or acorn pearly mussel, was a species of freshwater mussel, an aquatic

bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

mollusk in the family Unionidae. It is now

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

. This species was endemic 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 in the United States. Its natural habitat was riffle beds over gravel and sand. Like all other members of this sensitive genus, its population had severely declined to habitat destruction and pollution. The last remaining individuals were killed in the 1970s due to exposure to domestic sewage.NatureServe Explorer
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References

Bivalves described in 1834 Extinct invertebrates since 1500 Extinct bivalves haysiana Extinct animals of the United States Species made extinct by human activities Taxonomy articles created by Polbot {{Unionidae-stub