Body anteriorly truncate, posteriorly evenly tapering. Prostomium anteriorly rounded, posteriorly fused to segment 1. Dorsal pair of antennae longer than ventral pair. Median antenna small, often inserted in small hollow and difficult to detect. Eyes absent. Ciliated nuchal organs present ventrally on each side of mouth. Proboscis smooth with four long papillae in a subdistal ring. Tentacular cirri of segment 1 reaching about segments 4-5. Dorsal tentacular cirri of segment 2 reaching about segment 6. Ventral tentacular cirri as long as those of segment 1. Dorsal tentacular cirri of segment 3 the longest, reaching about segment 7. Segment 2 with 3-4 composite chaetae and an acicula situated in a pouch behind tentacular cirri of segment 1. Segment 3 with about ten broad hooded chaetae and an acicula without ventral cirri. Segment 4 ventrally with three stout hooks and an acicula, lacking parapodial lobes, with small dorsal and ventral cirri. Dorsal cirri of median segments oval, with cirrophores extending onto dorsal side of dorsal cirri. Extension of cirrophores not developed on anterior segments. Parapodial lobes narrow, with about fifteen chaetae. Terminal end of chaetal shaft asymmetrical with few teeth, one larger than the others. Blades long and slender. Ventral cirri oval, longer than parapodial lobes (C. nilssoni-detail). Pygidial cirri cylindrical, about four times as long as broad. Ciliation present on cirrophores, extending as transverse bands across the dorsum.
Preserved relaxed specimen 25 mm long for 95 segments.
Living animals yellowish, transparent. Preserved animals yellow to brown, dorsal and ventral cirri darker.
Mud bottoms. Recorded from 14 to 1100 m, mainly found below 70-80 m.
Iceland, West Mediterranean, northern North Sea, Norway and Skagerrak.