Members of this order have an elongated, segmented body and a distinct head, normally with a separate peristomium and prostomium.

Many, but not all, live in tubes which vary from a mucous sheath to a tough, horny casing.

There is a muscular pharynx with a dorsal pair of mandibles and a set of ventral, toothed, maxillary plates.

[3] It also had the biggest scolecodonts of any prehistoric polychaete, up to 13.2 mm (0.52 in) in length and possibly larger.

[3] The World Register of Marine Species (WoRMS) includes the following families in the order:[1]