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Bivalves can be divided into dimyarians that possess two adductor muscles and monomyarians that only possess one.Within the monomyarians, some are attached during their adult life while others are free living.Among the free living monomyarians, only the file shell and the scallops are capable of swimming movements.Scallops swims using water jet propulsion produced by a succession of abductions (opening) and adductions (closing) of the two valves (Olson and Marsh 1993).The adductor muscle closes the valves while the hinge ligament opens them (Trueman 1953; Alexander 1966).The scallop hinge ligament has an inner and an outer layer.The outer layer unites the two valves at the dorsal margin along the hinge.The inner layer has a pyramidal shape and its ventral base bulges when the valves are closed.This layer attaches the two valves and is composed of a rubber-like material which acts like a spring mechanism, allowing the opening of the valves when the adductor muscle relaxes (Alexander 1966).