English: Epioblasma personata (Say, 1829) - fine-rayed pearly mussel (CMC, Cincinnati Museum of Natural History & Science, Cincinnati, Ohio, USA)

Bivalves are bilaterally symmetrical molluscs having two calcareous, asymmetrical shells (valves) - they include the clams, oysters, and scallops. In most bivalves, the two shells are mirror images of each other (the major exception is the oysters). They occur in marine, estuarine, and freshwater environments. Bivalves are also known as pelecypods and lamellibranchiates.

Bivalves are sessile, benthic organisms - they occur on or below substrates. Most of them are filter-feeders, using siphons to bring in water, filter the water for tiny particles of food, then expel the used water. The majority of bivalves are infaunal - they burrow into unlithified sediments. In hard substrate environments, some forms make borings, in which the bivalve lives. Some groups are hard substrate encrusters, using a mineral cement to attach to rocks, shells, or wood.

The fossil record of bivalves is Cambrian to Recent. They are especially common in the post-Paleozoic fossil record.

Shown here is a rare freshwater bivalve shell of an extinct species, Epioblasma personata, the fine-rayed pearly mussel, also known as the round combshell.

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From museum signage:

Mussels of the Little Miami River

The Little Miami River flowing through the eastern portion of Cincinnati is a national scenic river. Of the nation's 4,000 rivers, only 165 have been honored with such a designation. A national scenic river is one that includes an "outstandingly remarkable" biologic community.

Displayed here are the 50 types of native mussels that have been recorded from the river and its tributaries. Nine of these species are no longer found in the Little Miami system due to water quality deterioration.

Water pollution has also caused the disappearance of 7 of the 113 fishes recorded from the river. With better control of soil erosion and improved treatment of sewage effluent, the missing mussel and fish species could return to the Little Miami basin.

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From museum signage:

Vanished Mussels of the Cincinnati Area

These animals are absent from the region's streams due to water pollution and the drowning of riffles behind dams.

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Classification: Animalia, Mollusca, Bivalvia, Palaeoheterodonta, Unionoida, Unionidae

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See info. at: en.wikipedia.org/wiki/Fine-rayed_pearly_mussel and

en.wikipedia.org/wiki/Epioblasma