Body long, thin, filamentous. Prostomium conical, fused to the anterior segments, without eyes. Anterior three achaetous segments dorsally more or less separated. One pair of thick palps on the anterior margin of the first chaetiger.
One filamentous gill dorsally on all notopodia from the first chaetiger to nearly the posterior end.
Numerous chaetae; all chaetae capillaries, the dorsal ones longer than the ventral ones.
Pygidium roundly triangular; anus dorsal, surrounded by 5 small papillae.
Up to 100 mm for 200 segments.
In mud; sometimes in sandy mud and between shells and stones.
Atlantic up to Mediterranean, English Channel, whole North Sea, Skagerrak, Indian Ocean, Australia, Chile, Antarctic.