Body small and slender.
Prostomium rounded, broader than long, with four eyes in a trapezoid arrangement, without ocelli. Palps broad, fused at the base, as long the prostomium. Median antenna twice as long as the lateral ones. Lateral antennae much longer than prostomium, without annulation. Dorsal tentacular cirri about as long as the lateral antennae; ventral tentacular cirri shorter, as long as or shorter than parapodial lobes. Dorsal cirri of all parapodia shorter than segment width. Ventral cirri about as long as or shorter than parapodial lobes. All appendages smooth.
All chaetae compound. Blades of upper chaetae twice as long as lower chaetae, bidentate (P. compacta-detail). Posterior parapodia without simple chaetae. Pharynx with 1 anterior tooth and 10 papillae.
Body up to 10 mm long for 50 segments.
Light with unregular dark spots dorsally and ventrally or with thin transverse green lines anteriorly.
Arctic, North Pacific, North Atlantic to Skagerrak.