Body elongated, sligthly tapering at both ends.
Prostomium quadrangular, incised posteriorly, with 4 eyes, anterior pair larger and with lenses. Prostomium with 2 antennae and 2 annulated palps, thicker and shorter than the antennae and with 2 rings.
Lateral antennae a little longer than the prostomium. Median antenna absent.
6 pairs of annulated tentacular cirri on 3 reduced segments.
Tentacular cirri of second segment the longest, reaching to about the 12th segment. Parapodia subbiramous, without dorsal chaetae. Tentacular and dorsal cirri annulated and with cirrophores, often including one acicula.
Dorsal cirri partly even longer than tentacular cirri. Ventral cirri short.
Notopodia consisting only of dorsal cirri and one acicula within the cirrophore. Neuropodia conical, with 2 aciculae and several compound chaetae, with long bidentate blades.
Pharynx with about 12 fringed terminal papillae, with 2 jaws and a bidentate stylet (S. armata-detail).
Pygidium with 2 annulated cirri, pygidial plate absent.
Body up to 9 mm for 29-38 segments.
Body yellowish, with fine cross-lines and a brown spot on the basis of the dorsal cirri.
On all substrata, eulittoral to about 50 m. Between seaweeds, sponges, serpulid-tube, also between stones and in sand.
Atlantic between the Hebrides and South Africa, Mediterranean, English Channel, Skagerrak.