Body long and thin, with numerous segments.
Prostomium conical, slightly longer than wide, flattened ventrally, usually without eyes. Peristomium of the same length as the following segments.
Parapodia with rudimentary dorsal cirri. Prechaetal lobe short, rounded; postchaetal lobe tongue-shaped, becoming erect in posterior segments. Several slender aciculae in the notopodia; neuropodia with several slender and one stout projecting acicula. Curved winged capillary chaetae.
Mandibles X-shaped, often absent. Maxillary carriers long, slender, separate, with a short oval or hexagonal unpaired median piece. Maxillae I: symmetrical, hooked forceps, smooth or toothed at base; maxillae II: slightly hooked, with 7-11 teeth on each maxilla; maxillae III: with 1-3 teeth on each maxilla; maxillae IV and V: unidentate, maxilla V often absent. Endoparasitic form often with reduced maxillae (D. filum-detail).
Up to 160 mm for numerous segments.
Yellowish, pink, or greenish grey, highly iridescent.
In sand, mud, mixtures of both, gravel, subtidally among Posidonia and Dendropoma to depths of about 2000 m. Besides the free-living form there is a form which is endoparasitic in cirratulid polychaetes, eg. Cirratulus cirratus .
Widely distibuted in the northern hemisphere, excluding the Arctic.