Body long and slender, dorsally arched, ventrally flattened. Anteriorly, slightly and posteriorly strongly tapering.
Prostomium often retracted, with four antennae. Four kidney-shaped eyes.
First segment with one pair of tubercles. Following segments dorsally with one transversal row of two big and two small tubercles with terminal papillae. Dorsal and ventral surface densely papillated.
First segment with short parapodia, without chaetae. Following segments with short papillated parapodia and a conical terminal papilla. Ventral cirrus with a terminal papilla. Dorsal cirrus large and rounded with a terminal papilla. Chaetae simple with subdistal swelling and one colourless acicula (S. flavum-detail).
Pygidium with 2 round papillae.
Proboscis densely papillated.
Up to 60 mm long for 120 segments.
Anterior part yellowish, posterior part brownish yellow, pink or lilac.
On all substrata, from eulittoral to 1400 m deep.
Whole North Sea, Skagerrak, Kattegat, Öresund, Arctic, Antarctic.