File:Ensis siliqua (giant razor clam).jpg

English: Ensis siliqua Linnaeus, 1758 - giant razor 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 giant razor clam shown above is part of the Lusitanian Province: "Concentrated in the mild temperatures of the Mediterranean Sea, and extending to the warmer waters of the Canary Islands and the cooler areas of France and Great Britain, is a fairly rich fauna. These waters support dozens of unique species, such as Jacob's scallop, the oxheart cockle and the European pelican's foot." [info. from museum signage]

The thin brown crust partly covering the giant razor clam shells shown above is an organic layer called the periostracum.

Classification: Animalia, Mollusca, Bivalvia, Heterodonta, Veneroida, Pharidae

Locality: unrecorded/undisclosed/unspecified

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More info. at: en.wikipedia.org/wiki/Ensis and

en.wikipedia.org/wiki/Pod_razor