Highly mobile animals with long slender bodies and many segments. Prostomium with 4 or 5 pairs of antennae. Peristomium with 2-4 pairs of tentacular cirri. Parapodia are usually uniramous with the notopodium represented by the expanded foliose dorsal cirri which characterise the family. Neurosetae are compound and (if present) notosetae simple.