The grooved carpet shell, or Palourde clam, Ruditapes decussatus, or Venerupis decussatus, is a clam (bivalve mollusc) in the family Veneridae. It is distributed worldwide and due to its ecological and economic interest has been proposed as a 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 into the down-sloping anterior margin. It is prominent posteriorly, where the shell is conspicuously decussate. The surface has a sculpture of fine concentric striae and bolder radiating lines. Growth stages are clear. The lunule and escutcheon are poorly defined. Each valve has three cardinal teeth: the centre one in the left valve, and centre and posterior 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.
