Bivalvia

Bivalvia, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. Bivalves as a group have no head and they lack some usual molluscan organs like the radula and the odontophore. They include the oysters, cockles, mussels, scallops, and numerous other families. The majority are filter feeders. The gills have evolved into ctenidia, specialised organs for feeding and breathing. Most bivalves bury themselves in sediment where they are relatively safe from predation. Others such as the scallops lie on the sea floor or attach themselves to rocks or other hard surfaces. The scallops and the file shells can also swim. The shipworms bore into wood, clay, or stone and live inside these substances.

Bivalves have long been a part of the diet of coastal and riparian human populations. Oysters were cultured in ponds by the Romans, and mariculture has more recently become an important source of bivalves for food. Modern knowledge of molluscan reproductive cycles has led to the development of hatcheries and new culture techniques. A better understanding of the potential hazards of eating raw or undercooked shellfish has led to improved storage and processing. Pearl oysters (the common name of two very different families in salt water and fresh water) are the most common source of natural pearls. The shells of bivalves are used in craftwork, and the manufacture of jewellery and buttons. Bivalves have also been used in the biocontrol of pollution.