Worms with smooth tapering cylindrical bodies living in tough non calcareous tubes. The prostomium and peristomium are fused and have developed into a tentacular crown (bi-pinnate radioles) that often obscures a pair of grooved palps. There is no operculum. The peristome is often developed into a collar surrounding the base of the radioles. The body is clearly divided into thorax and abdomen. Chaetae are winged capillaries and uncini. Note that the tentacular crown is easily lost during collection and preservation.