(M. Sars, 1835)
Body broad, flattened, of uniform width, covered by dorsal cirri. Prostomium rounded. Median antenna larger than paired ones, situated between eyes. Eyes large, rounded. Proboscis long, rather thin, broader distally; proximal part with two groups of about 4-5 dorso-lateral papillae, often covered by the prostomium, and a row of lateral papillae on each side. Lateral rows enlarge distally and cover entire distal proboscis. Nuchal epaulettes varying in shape, more or less distinctly bilobed. Ciliation on prostomium, forming a band running from base of median antenna back to nuchal organs, on nuchal organs, and as single bands on each segment. Segment 1 not visible dorsally. Tentacular cirri of segment 1 reaching about segments 3-4. Dorsal tentacular cirri of segments 2 and 3 reaching about segment 11. Ventral tentacular cirri slightly flattened, reaching about segment 4. Chaetae present from segment 2. Dorsal cirri of median segments much broader than long. Dorsal cirrophores with an acicula and 1-2 capillaries present from about segment 15. Parapodial lobes with large number of compound chaetae. Terminal end of chaetal shaft with large number of teeth, decreasing in size proximally. Blades rather long and slender. Ventral cirri broad, rounded, directed obliquely upwards (N. foliosum-detail). Pygidial cirri flattened. Minute median pygidial papilla present.
Up to 60 mm for 115 segments.
Living animals yellow with more or less dense patches of darker blackish brown pigmentation on dorsal cirri. Dorsum iridescent. Red spots on ventral, and occasionally dorsal, cirrophores. Eyes dark brown. Preserved animals much darker, dorsal cirri often attaining an almost black. Eyes blackish.
Subtidally on bottoms with sand, shell gravel and stones. Recorded to 1750 m.
Reported as circumboreal.