Anatomy - Body Wall, Coelom and Locomotion

The earthworm's body wall lies just beneath a thin, moist cuticle and consists of an epidermis (with supporting, gland, basal and sensory cells), an outer layer of circular muscle, an inner layer of longitudinal muscle, and an innermost coelomic epithelium. Between this body wall and the alimentary canal is a large fluid-filled cavity, the coelom, containing coelomic fluid rich in cells (coelomocytes) that assist regeneration, immunity and wound healing. Because this fluid cannot be compressed, it acts as a hydrostatic skeleton against which the muscles can push. Locomotion results directly from this arrangement: contraction of the circular muscles makes a segment long and thin, while contraction of the longitudinal muscles makes it short and thi …