Body broad, flattened, posteriorly tapered. Prostomium oval. Median antenna larger than paired ones, situated between eyes. Eyes large, rounded. Proximal part of the proboscis with two groups of two big and a few small dorso-lateral papillae. Nuchal epaulettes each with 6-10 lobes. Longest tentacular cirri reaching about segments 9.
Dorsal cirri of median segments kidney-shaped, twice as broad as long. Dorsal cirrophores from chaetiger 13 onward with one or two aciculae and a capillary chaeta. Parapodial lobes with about 35 compound chaetae. Ventral cirri similar to dorsal cirri (N. americanum-parapodium). Pygidial cirri oval to finger-like.
50 mm for 125 segments.
Living animal dorsally iridescent, dark brown-black, ventrally blue.
Massachusetts (USA), one specimen found in the Skagerrak.