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Temporal range: Tremadocian–0 [1]
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Mollusca
Class: Bivalvia
Subclass: Heterodonta
Order: Anomalodesmata
Dall, 1889

See text.



Anomalodesmata is an order of saltwater clams, marine bivalve molluscs. [2] 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. [3]



The shells of species in this order are of equal size, as are the muscles that hold them closed, and the margins at the hinges are thickened. The margins of the mantle are also fused, and there is only a single hinge tooth, if any. [4]


In 2010, a new proposed classification system for the Bivalvia was published in Malacologia by Bieler, Carter & Coan revising the classification of the Bivalvia, including the order Anomalodesmata. [5] The following tree is their info which has been updated with the latest information from the World Register of Marine Species:

Order: Anomalodesmata

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Ostreida order of molluscs

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.

Arcida order of molluscs

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.

Pteriida order of molluscs

The Pteriida are an order of large and medium-sized marine bivalve mollusks. It includes five families, among them the Pteriidae.

Pteriomorphia subclass of molluscs

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 subclass of molluscs

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 Subclass of molluscs

Heterodonta is a taxonomic subclass of saltwater clams, marine bivalve molluscs. This subclass includes the edible clams, the cockles and the Venus clams.

Trigonioidea superfamily of molluscs

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 family of molluscs

Nuculidae is a family of small saltwater clams in the order Nuculida. Species in this family are commonly known as nut clams.

Mytilida order of molluscs

Mytilida is an order of marine bivalve molluscs, commonly known as true mussels. There is one extant superfamily, the Mytiloidea, with a single extant family, the Mytilidae.

Hiatellidae family of molluscs

Hiatellidae is a taxonomic family of saltwater clams, marine bivalve molluscs. This family is placed in the order Adapedonta.

Pectinoidea superfamily of molluscs

The Pectinoidea are a superfamily of marine bivalve molluscs, including the scallops and spiny oysters.

Protobranchia subclass of molluscs

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.

Fordilloidea superfamily of molluscs (fossil)

Fordilloidea is an extinct superfamily of early bivalves containing two described families, Fordillidae and Camyidae and the only superfamily in the order Fordillida. The superfamily is known from fossils of early to middle Cambrian age found in North America, Greenland, Europe, the Middle East, Asia, and Australia. Fordillidae currently contains two genera, Fordilla and Pojetaia each with up to three described species while Camyidae only contains a single genus Camya with one described species, Camya asy. Due to the size and age of the fossil specimens, Fordillidae species are included as part of the Turkish Small shelly fauna.

Poromyoidea is a superfamily of molluscs. It used to contain only the family Poromyidae, but now it also contains Cetoconchidae Ridewood, 1903, as CetoconchaDall, 1886 was removed from Poromyidae and given its own family, according to the World Register of Marine Species.

2010 Bivalvia taxonomy Classification of bivalve molluscs according to some authorities

In May 2010, a new taxonomy of the Bivalvia was published in the journal Malacologia. The 2010 taxonomy is known as the Taxonomy of the Bivalvia . The 2010 taxonomy was published as Nomenclator of Bivalve Families with a Classification of Bivalve Families. This was a revised system for classifying bivalve mollusks such as clams, oysters, scallops, mussels and so on. In compiling this new taxonomy, the authors used a variety of phylogenetic information including molecular analysis, anatomical analysis, shell morphology and shell microstructure, as well as bio-geographic, paleobiogeographical and stratigraphic information.

Mytiloidea superfamily of saltwater clams

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.

Carditida Order of molluscs

Carditida is an order of marine bivalve clams.

Carditoidea Superfamily of molluscs

Carditoidea is a superfamily of marine bivalve clams.


  1. Sánchez, T. M.; Vaccari, N. E. (2003). "Ucumariidae new family (Bivalvia, Anomalodesmata) and other bivalves from the Early Ordovician (Tremadocian) of northwestern Argentina". Ameghiniana. 40 (3): 415–424. doi:10.5710/amgh.v40i3.969.
  2. Anomalodesmata Stoliczka, Dall, 1889 . Retrieved through: World Register of Marine Species  on 9 July 2010.
  3. "WoRMS - World Register of Marine Species - Anomalodesmata". Retrieved 2019-04-03.
  4. Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. p. 431. ISBN   0-03-056747-5.
  5. Bieler, R., Carter, J.G. & Coan, E.V. (2010) Classification of Bivalve families. Pp. 113-133, in: Bouchet, P. & Rocroi, J.P. (2010), Nomenclator of Bivalve Families. Malacologia 52(2): 1-184