Body long, cylindrical, very fragile.
Prostomium short, conical, with 2 groups of small eyes and 2 nuchal organs.
Thorax with 12 segments; thoracic segments with a reticulated integument. First segment without chaetae, following 11 segments with capillary chaetae only.
Posterior body with hooded hooks, between dorsal and ventral rami on each side (N. latericeus-detail).
Simple gills are formed by extensions of the rami along most of the posterior region; gills not retractile.
Paired genital pores dorsally on numerous (7-12) anterior segments of the posterior region; genital hooks absent.
Pygidium terminates in a membranous flap; without cirri.
Up to 300 mm for 150 segments.
Anterior body red or yellowish-red; posterior body transparent.
Lower eulittoral down to 7216 m deep, especially in Arctic and Antarctic regions.
Cosmopolitan. North Sea, Skagerrak and Kattegat.