In Ascaris, locomotion is poor because their body wall lack circular muscles. Ascaris (round worms) consitute the phylum-Aschelminthes. They may be free-living, aquatic and terrestrial or parasitic in plants and animals. In Ascaris, the epidermis is either a syncytium or a single layer of cells and is covered by a thick collagenous cuticle. The cuticle is often of complex structure and may have two or three distinct layers. Underneath the epidermis lies a layer of longitudinal muscle cells. The relatively rigid cuticle works with the muscles to create a hydroskeleton as they lack circumferential muscles.