The musculature comprises entirely longitudinal fibres, which are laid as bands with a contractile and non-contractile component. The nematodes lack a true brain, instead having a commisure of anterior ganglia surrounding the pharynx. These ganglia give rise to a dorsal and ventral nerve cord that run longitudinally down the trunk, closely associated with the body wall. Sensory structures include papillae , located on the rostral and caudal cuticular surfaces. More specialised organs include amphids, which are internal cephalic pits lined with sensory hairs that are connected by lateral openings to the exterior of the organism.
Phasmids are organs of similar arrangement found in the posterior of many parasitic nematodes.
The hypodermal cell nuclei occur on four inward projections called hypodermal cords , which run longitudinally down the dorsal, ventral and lateral aspects of the body. The dorsal and ventral hypodermal cords support the associated nervous tissue. The lateral cords may hold the nematodes lateral excretory canals. The pseudocoel is more pronounced in some species than others. Where it is prominent, it serves as a hydrostatic skeleton, transferring the forces applied by the longitudinal muscles, and allowing movements to be generated.