File:Panopea generosa (Pacific geoduck clam) 1.jpg

English: Panopea generosa Gould, 1850 - Pacific geoduck clam (public display, Bailey-Matthews Shell Museum, Sanibel Island, Florida, 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.

The Pacific geoduck clam shown above is part of the Oregonian Province: "The cool-water Oregonian Province along the Pacific Northwest Coast lies between the frigid Aleutian Province of Alaska and the warmer Southern Californian and Panamic Provinces. Because of harsh coastal conditions, most gastropods do not do well here. Bivalves at quieter depths predominate. The shells are fewer in kinds, lacking the bright colors, but occur in great numbers." [info. from museum signage]

Classification: Animalia, Mollusca, Bivalvia, Heterodonta, Myoida, Hiatellidae

Locality: unrecorded/undisclosed/unspecified

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More info. at: en.wikipedia.org/wiki/Panopea_(bivalve) and

en.wikipedia.org/wiki/Geoduck