Abstract
It is shown that the queen scallop Chlamys (Aequipecten) opercularis effectively retains particles down to about 7 µ in diameter. Below this limit the retention efficiency decreases and reaches zero for particles of about 1.6 µ in diameter. This is a markedly lower efficiency than in Mytilus edulis. It is suggested, that the queen scallop compensates for the loss of these particles by a high pumping rate and low metabolic requirements.