The grooved carpet shell or Clam clam ,  Ruditapes decussatus , is a clam or bivalve mollusc in the family Veneridae . It is distributed worldwide and due to its ecological and bioindicator .
This species is one of the most popular and profitable mollusc of lagoonal and coastal sites in the Mediterranean, where it was collected for a long time as food. It is consumed fresh and canned.
The shell is broadly oval to quadrate with the umbones distinctly anterior. The posterior hinge line is straight, the posterior margin truncate, and the anterior hinge line grades in the down-sloping anterior margin. It is prominent later, where the shell is conspicuously decussate. The surface has a sculptureof concentric striae and bolder radiating lines. Growth stages are clear. The lunula and escutcheon are poorly defined. Each valve has three cardinal teeth: the center in the left valve, and center and later in right are bifid. The pallial line and adductor scars are distinct. The pallial sinus is U-shaped, not extending beyond the midline of the shell, but reaching a point below the posterior part of the ligament. The lower limb of the sinus is distinct from the pallial line for the whole of its length. The inner surfaces of the shell are glossy white, often with yellow or orange tints, and with a bluish tinge along the dorsal edge. The overall color is cream, yellowish, or light brown, often with darker markings. 
Despite improper management, some regions in the Atlantic coast of the Iberian Peninsula , and the Mediterranean basin , Ireland , currently have solid populations of Ruditapes decussatus .   
Ruditapes decussatus is cultured from the Atlantic coast of France , Spain , Portugal and the Mediterranean basin . It is often grown with other bivalves ( Venerupis pullastra , Venerupis rhomboideus , Venerupis aurea , Dosinia exoleta and Tellina incarnate ). Their predators are shore crabs ( Carcinus maenas ); starfish ( Asterias rubens and ice-cold Marthasterias ); gastropods (Natica sp.); and birds (Larus sp). An individual Carcinus maenas(6.5 cm width) can consume 5 gold 6 clams per day. Marine aquaculture production of grooved carpet shell in 2003 was 3,007 t in Portugal, which excludes non-aquaculture harvesting of the species.
Between 1997 and 2001 total aquaculture production varied between 3,700 and 4,900 tonnes, from five countries. Most were produced by Portugal but France and Spain have also been significant producers; however, the contribution from France is now much less than before; in 1995 it was by far the leading producer with nearly 5,200 tons but in 2004 it produced only 475 tons. Global production seems to be declining; in 2004 it was only 2,700 tons but the United Kingdom had appeared as a minor producer.
In 1985 the price for live Ruditapes decussatus was about € 0.60 / kg. In 2005, the price was about € 15 / kg. It is consumed fresh and canned. 
- ^ Jump up to:a b Ruditapes decussatus (Linnaeus, 1758) World Register of Marine Species. Retrieved 2011-10-06.
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- ^ Jump up to:a b c FAO Species Identification and Data Program (SIDP) – Fisheries and Aquaculture Department
- Jump up^ FAOSpecies Fact Sheets Ruditapes decussatus
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