Two communities of the recent bivalveCardium edule L. were collected in the tidal flats near List on the island of Sylt (Southern North Sea). The cockles were examined for abrasion marks on the surfaces of their valves arising from various causes. One important group of abrasions reveals traction marks restricted to the beak region, caused exclusively by valve movements. Another group is characterized by marks due to shell abrasions on the sea bed. The various types of abrasion marks have been studied in living cockles, both in the sea and in laboratory containers, and the results compared with those obtained on dead ones still connected by the ligament. In the sea, livingCardium edule were studied via Scuba-observations. Traction marks on the umbo support the conclusion that living cockles sometimes rest on their dorsal shell area. Holes in the convex umbo, umbonal facets, originate after death in situ or through shiftings to and fro on the sea bed, and also as a result of chemical or biological processes. The method applied and the criteria of shell abrasions employed are considered acceptable approaches to the interpretation of functional morphology and behaviour in fossil molluscs.