File:Spondylus princeps (Pacific thorny oyster) 2.jpg

English: Spondylus princeps Broderip, 1833 - Pacific thorny oyster (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 thorny oyster shown above is part of the Panamic Province: "Much richer in species than its Caribbean counterpart, the tropical-water Panamic area extends from the Gulf of California, along the Pacific coast of Central America to Ecuador. Known for its wide tidal ranges, its sandy-mud shores and offshore waters abound in colorful murexes, cones, olives and cowries. Over 2,500 species are known from here, including the endemic tent olive." [info. from museum signage]

Classification: Animalia, Mollusca, Bivalvia, Pteriomorphia, Pectinoida, Spondylidae

Locality: unrecorded/undisclosed/unspecified

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More info. at:

en.wikipedia.org/wiki/Spondylus