Ark clam
Anadara from the Pliocene of Cyprus.
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Bivalvia
Subclass:	Pteriomorpha
Order:	Arcoida
Family:	Arcidae Lamarck, 1809
Genera
See text

Ark clam is the common name for a family of small to large-sized edible saltwater clams or marine bivalve molluscs in the family Arcidae. Ark clams vary both in shape and size. They number about 200 species worldwide.

The shells of ark clams are often white or cream, but in certain species, the shell is striped with, tinted with, or completely colored with a rich brown. In life the shell of most species has a thick layer of brown periostracum covering the harder calcareous part of the shell. In some genera such as Barbatia, the periostracum can be tufted at the end of the shell into something that resembles a beard, hence the name Barbatia or bearded one.

The group is known as "ark shells" because genera such as Arca have a large flat area in front of the umbo, which, in an intact shell, can somewhat resemble a deck, with the rest of the shell perhaps resembling an ancient keeled boat such as Noah's ark is thought to have been.

All ark shells have a long straight hinge line with a single row of numerous small and unspecialized "teeth". This is known as a "taxodont dentition" and represents an ancient lineage. This kind of hinge line is also found in the bivalve families Glycymerididae, Nuculidae and Nuculanidae.

The thick outer skin or periostracum of an ark clam can act as camouflage, such that the shells can sometimes look like stones when lying on the bottom.

Large ark clams, such as Arca zebra, are commonly used as bait, as well as food, throughout the Caribbean.

[edit] Genera

Numerous valves of arcids, genus Senilia, washed up on the beach in Senegal

Genera within the family Arcidae include:

• Acar Gray, 1857
• Anadara Gray, 1847
• Arca Linnaeus, 1758
• Barbatia Gray, 1847
• Bathyarca Kobelt, 1891
• Bentharca Verrill and Bush, 1898
• Samacar Iredale, 1936
• Scapharca
• Senilia
• Trisidos

[edit] External links

Wikispecies has information related to: Arcidae

• ITIS
• Archerd Shell Collection, Ark clams