Prostomium short, subconical, with a pair of ovoid or awl-shaped frontal palps and a pair of cushion-like ventral palps. Antennae with a few faint basal rings. Two large eyes external to the bases of the dorsolateral posterior antennae and two minute eyes posterior to the frontal antennae. Peristomium somewhat shorter than the following chaetigers, with a pair of slender and cylindrical peristomial cirri near the anterior margin (N. conchylega-anterior end).
Chaetiger 1 longer than the following chaetigers, with greatly enlarged and anteriorly directed parapodia. Parapodia of chaetiger 2 and 3 slightly enlarged. Dorsal cirri slender and cylindrical, in the first 20 chaetigers or so as long as the gills, then shorter. Ventral cirri of the first two parapodia slender and cylindrical, the rest globular or pad-like (N. conchylega-parapodium). Pygidium with a pair of long cirri. Gills simple (rarely with two filaments), beginning on chaetigers 9-13 and continuing to near the end of the body. First two parapodia with winged capillary chaetae and simple stout hooks. Chaetiger 3 with capillary chaetae and pseudoarticulate unidentate or bidentate hooded hooks. Rest of parapodia with capillary chaetae, comb-chaetae, and one or two stout bidentate hooded hooks starting on chaetigers 9-12. Chaetae and aciculae light amber-coloured (N. conchylega-chaetae).
Mandibles X-shaped. Maxillary carriers short. Maxilla I: hooked forceps; maxilla II: 7-12 teeth each; maxilla III: 8-10 teeth; maxilla IV: 5-9 teeth each (N. conchylega-jaw plates).
Up to 150 mm for 150 segments.
Elongate rectangular, greatly flattened, scabbard-shaped; parchment-like lining completely covered by small, angular, flattened fragments of shells, stones, pebbles.
Variable, bluish with red transverse bands; whitish yellow with violet brown stripes, with rust coloured spots on bases of parapodia and cirri.
At low water and dredged on bottoms of sand, gravel, mud, and various mixtures of mud, sand, broken shells and rocks to depths of 4020 m. The tube lies free on the surface and is transported with the worm when it forages.