The feeding mechanism of Recent Acrothoracica (Cirripedia, Crustacea) is described. The slits of fossil Acrothoracica are compared with those of Recent representatives. The metamorphosis of the cypris larva of the Acrothoracica is seen in contrast to that of other barnacles (Balanidae, Thoracica). It is shown that the orientation of cirriped borings cannot be derived from the direction of the water current bringing the food to the adults. It is the behaviour of the cypris during fixation which is responsible for a uniform orientation of the adults. The feeding habits and larval development of cirripeds suggest the idea that the belemnites, like recent cephalopods, generally swam by means of the rocket principle.