Bands of oblique muscle are associated with parapodium function. Also in contrast to the earthworms, polychaetes like the clam worm have much more of a head, including a prostomium with four eyes, two tentacles, two palps, and the peristomium has four pairs of tentacles in addition to the oral apparatus. These tentacles can become ciliated in tube worms for filter feeding. Mostly fresh water, leeches have dorsal-ventrally flattened bodies with suckers on each end. Instead of internal septa, many are full of connective tissue and muscle in oblique as well as circular and longitudinal bands.
Leeches can swim with dorsoventral undulations.
On a solid surface, leeches move as one unit, first attached by the larger posterior sucker, then reaching out with smaller anterior sucker. Use of anticoagulant in saliva keeps blood flowing. Evolutionary relationships of annelids. Differences between the arthropods and annelids can be explained in terms of the cuticle characteristics and locomotion. R Buchsbaum et al.