Structure of locomotory appendages of Caligidae (Copepoda: Caligoida) is briefly reviewed from the point of view of functional morphology. Locomotory mechanisms are studied on examples of Lepeophtheirus salmonis and Caligus clemensi. Rapid propulsion is attributed to antagonistic movements of the first two pairs of legs, the second pair being a more important contributor. Beating towards each other, the legs produce a jet of water, which propels the parasite. In a subsequent recovery stroke, the second leg, made watertight by a dorsal membrane, gives further impetus to the jet, pushing it out through the sinus opening of the cephalothorax. Water is replenished under the cephalothorax by intake via space under the frontal plates. Settling movements help to improve the grip of the parasite on the host's surface and involve rapid side-to-side motion, involving the second maxillae. Steering is carried out by lateral and vertical movements of the posterior part of the body. Functions of other appendages are discussed.