-They have elongated cylindrical body
-They are triploblastic
-They are metamerically segmented
-Their body walls consist of thin cuticle
-They possess an outer layer of circular muscle and inner layer of longitudinal muscles
-Possesses gut, which is straight and ends in the anus
-Digestion is extracellular
-Excretory organ is nephridia
-Possess closed blood system
-Nervous system consists of a dorsal brain
-Appendages when present are never jointed
-Larva when present is trochophore
-Locomotive organ is chaetae
-Undergoes cephalization, although head in not very distinct
-Nephridia are segmentally arranged
-Body is divided into three parts
-In the body layer, the mesoderm is divided into two layers-somatic mesoderm and splanchnic mesoderm