Large elongate worms. Prostomium usually with 2 pairs of antennae but always with a pair of bi-articulate palps. Peristome with usually 4 but sometimes 3 pairs of tentacular cirri. Eversible pharynx with a pair of jaws; some genera armed with many chitinous paragnaths or papillae, while in several genera pharynx unarmed. Parapodia uniramous for first two setigers then usually biramous but some genera uniramous throughout. Most genera usually without branchiae/gills; where branchiae occur usually branched and arise on mid anterior segments of body. Setae mainly compound, both falcigers and spinigers.