Body covered with tiny papillae, which are encrusted with sand and mud.
Prostomium rounded quadrangular to semicircular, broader than long, not clearly separated from the peristomium. With four big, blackish eyes, with lenses, in a rectangular arrangement, ocelli absent. Palps triangular, fused, longer than the prostomium, broadly divided by a median groove. Lateral antennae flask-shaped, a little shorter than palps. Median antenna similar, a little longer.
Tentacular cirri as the lateral antennae in size and shape.
Dorsal cirri like tentacular cirri, about as long as parapodial lobes and absent on second parapodium. Ventral cirri finger-like, almost as long as parapodial lobes. From chaetiger 4 onwards, a large bulb-shaped gland above the parapodia.
Aciculae sharply pointed and hooked. Blades of compound chaetae moderately long and short, unidentate, with a fine denticulation along the border.
Middle and posterior parapodia with one upper and one lower unidentate simple chaeta (S. hystrix-detail).
Pygidium with flask-shaped cirri.
Body up to 5 mm long for 40 segments.
Transparent to light grey. Pharynx greenish.
From eulittoral to 800 m, between seaweeds, stones Amphioxus -gravel.
English Channel, North Sea and Skagerrak, probably cosmopolitan except Arctic and Antarctic.