The order Ostreida includes the true oysters. One superfamily (Ostreacea) and two families are recognised within it. The two families are Ostreidae, the true oysters, and Gryphaeidae, the foam oysters.
The Arcida is an extant order of bivalve molluscs. This order dates back to the lower Ordovician period. They are distinguished from related groups, such as the mussels, by having a straight hinge to the shells, and the adductor muscles being of equal size. The duplivincular ligament, taxodont dentition, and a shell microstructure consisting of the outer crossed lamellar and inner complex crossed lamellar layers are defining characters of this order.
The Pteriida are an order of large and medium-sized marine bivalve mollusks. It includes five families, among them the Pteriidae.
Rudists are a group of extinct box-, tube- or ring-shaped marine heterodont bivalves belonging to the order Hippuritida that arose during the Late Jurassic and became so diverse during the Cretaceous that they were major reef-building organisms in the Tethys Ocean, until their complete extinction at the close of the Cretaceous.
The Pteriomorphia comprise a subclass of saltwater clams, marine bivalve molluscs. It contains several major orders, including the Arcida, Ostreida, Pectinida, Limida, Mytilida, and Pteriida. It also contains some extinct and probably basal families, such as the Evyanidae, Colpomyidae, Bakevelliidae, Cassianellidae, and Lithiotidae.
Palaeoheterodonta is a subclass of bivalve molluscs. It contains the extant orders Unionida and Trigoniida. They are distinguished by having the two halves of the shell be of equal size and shape, but by having the hinge teeth be in a single row, rather than separated into two groups, as they are in the clams and cockles.
Heterodonta is a taxonomic subclass of saltwater clams, marine bivalve molluscs. This subclass includes the edible clams, the cockles and the Venus clams.
Trigonioidea is superfamily of medium-sized saltwater clams, marine bivalve molluscs. Within the fossil record the occurrence of this superfamily is widespread, ranging from the Devonian Period to Recent.
Nuculidae is a family of small saltwater clams in the order Nuculida. Species in this family are commonly known as nut clams.
Mactridae, common name the trough shells or duck clams, is a family of saltwater clams, marine bivalve mollusks in the order Venerida.
Unionida is a monophyletic order of freshwater mussels, aquatic bivalve molluscs. The order includes most of the larger freshwater mussels, including the freshwater pearl mussels. The most common families are the Unionidae and the Margaritiferidae. All have in common a larval stage that is temporarily parasitic on fish, nacreous shells, high in organic matter, that may crack upon drying out, and siphons too short to permit the animal to live deeply buried in sediment.
Anomalodesmata is an order of saltwater clams, marine bivalve molluscs. This grouping was formerly recognised as a taxonomic subclass. It is called a superorder in the current World Register of Marine Species, despite having no orders, to parallel it with sister taxon Imparidentia, which does have orders.
Chamidae, common name the jewel boxes or jewel box clams, is a taxonomic family of saltwater clams, the marine bivalve mollusks in the order Venerida.
Argopecten is a genus of saltwater clams, or scallops, marine bivalve mollusks in the family Pectinidae.
Protobranchia is a subclass of bivalve molluscs. It contains the extant orders Nuculanida, Nuculida, and Solemyida.
Pectinida is a taxonomic order of large and medium-sized saltwater clams, marine bivalve molluscs, commonly known as scallops and their allies. It is believed that they began evolutionarily in the late Middle Ordovician epoch; many species, of course, are still extant.
Chama is a genus of cemented saltwater clams, marine bivalve molluscs in the family Chamidae, the jewel boxes.
Mytiloidea are a superfamily of small to large saltwater mussels, marine bivalve molluscs in the order Mytilida.
Lucinida is a taxonomic order of saltwater clams, marine bivalve molluscs.
Carditoidea is a superfamily of marine bivalve clams.
