Bilateral,3 germ layers, pseudo coelomate (only)when cut down the middle both sides are identical. Taxonomic level: phylum Nematoda; grade of construction: organs derived from three tissue layers; symmetry: bilateral; type of gut: complete; type of body cavity other than gut: pseudocoel; segmentation: absent; circulatory system: present; nervous system: small bundles of nerves (ganglia), two nerve cords; excretion: special excretory cells.
Other features: small free-living and parasitic worms with only longitudinal muscles, circular in cross section; covered by cuticle; both free-living and parasitic. They have an excretory canal on both sides as well as a main nervous system. Have a cuticle to protect their epidermis(skin).
Nematodes are bilaterally symmetrical, elongate, and usually tapered at both ends. Some species possess a pseudocoel , a fluid-filled body cavity between the digestive tract and the body wall. Like arthropods and members of six other phyla, nematodes secrete an external cuticle that is periodically molted. These animals have been provisionally grouped together as the Ecdysozoa , a taxonomic category based on the assumption that molting has evolved only once. So far, gene sequence data from several molecules support such an assumption.