File:Dinocardium robustum (Atlantic giant cockle shell) (Sanibel Island or Cayo Costa Island, Florida, USA) 3.jpg

English: Dinocardium robustum Lightfoot, 1786 - Atlantic giant cockle shell (modern) from Florida, USA. (8.55 cm across at it widest)

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.

This is the interior surface of an Atlantic giant cockle shell. The many circular areas are barnacle encrustation scars. The barnacles occupied the surface after the cockle died and the soft parts were scavenged or decayed away.

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

Locality: beach on Sanibel Island or Cayo Costa Island, southwestern Florida, USA

---

See info. at:

en.wikipedia.org/wiki/Dinocardium_robustum