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Types of Bivalve Shellfish

Bivalve shellfish are classified as "bivalve" because they have two hinged halves, or valves. Clams, oysters, scallops and mussels are all bivalve shellfish. The term "shellfish," while applied to a variety of marine and freshwater life, is a commonly accepted misnomer. Bivalves are actually mollusks. Oysters and mussels spend their lives rooted to one spot, while clams bury themselves into sediment, while scallops move around by means of a muscle that ejects water and acts as a propellant.

Clams
- Edible clams, like other bivalves, are high in protein.
  
  Clams, such as the northern quahog and the littleneck clam, are bivalves that use a protruding muscle called a foot to bury into sediment. Of the myriad species of clam, many are edible. A clam's exoskeleton, or shell, comprises two matching valves adjoined by a ligament and held shut by adductor muscles on either side of the shell. Clams reach up from their holes to feed using two siphons. One siphon is used to draw in water, which then passes over gills that remove food particles and oxygen. The clam then expels waste with the rest of the water from the other siphon.
Oysters
- Edible oysters are actually in a completely different family from that of their pearl-producing compatriots.
  
  Oysters are bivalve mollusks that typically live in marine and brackish waters. While still larvae, these creatures attach themselves to any surrounding hard surface and become rooted in place. Oysters spend their entire lives in these rooted stations. Like clams, they filter water for nutrients, but unlike clams, they do so by opening and closing their shells. Many cultures prize edible oysters as a delicacy. These oysters can be eaten either cooked or raw.
Scallops
- The scallop shell is prized for its appearance and is often used as an artistic motif.
  
  Unlike the other types of bivalves, scallops can swim. Scallops possess a muscle that, when threatened, can propel the animal through the water to safety. Yet even though they are capable of this clever kind of jet propulsion, scallops spend the vast majority of their time sitting on the seafloor, filtering water for food. Scallops also differ from other bivalves in that they have a set of small, crude eyes that surround their shells.
Mussels
- Many species of mussel, both freshwater and marine, are harvested and eaten.
  
  Mussels are a type of bivalve similar to clams. Some mussel species live in fresh waters such as rivers and streams, while some species live in marine waters of bays and harbors. Like oysters, mussels attach themselves to a solid object while young and spend most of their lives rooted to the spot. However, a mussel in its youth can detach from its roost and move around some. Mussels are similar to pearl oysters in that they can in some cases produce small pearls.

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