The behaviour and the feeding mechanism of several species of the Arcturidae (Valvifera, Isopoda) is demonstrated. These isopods are characterized by a hemisessile way of living, they swim only occasionally. The animals keep contact with the substrate by means of the posterior legs (pereopods 5-7), whereas the filter legs (pereopods 2-4) are spread out into the water current. The first pereopod is shorter and more compact than the subsequent ones and functions as a cleaning leg. It serves to comb the filter legs and to pass the food particles over to the mouth parts.