Body of this scale-worm long, thin, tapering posteriorly. Dorsal surface smooth with a small ctenidium on the first segment, and ventral surface smooth.
Prostomium rounded, with a median antenna with large basal joint with an ear-shaped process on either side, two pairs of eyes the posterior pair on the anterior margin the anterior pair on the ventral surfaces. First segment with numerous capillary chaetae, a pair of small lateral antennae extending terminally, a pair of small ctenidia on the mid-dorsal surface, a pair of broad lamellae on the inner surface, and a pair of long dorsal and short ventral tentacular cirri. Scales overlap covering the body. They occur on segments 1, 3, 4 and 6, then alternately to the 26th and then on all segments. The first pair are round, the next 11-14 pairs kidney shaped, with a few forked papillae on the outer margin, and smooth surfaces, the remaining scales with a notched outer margin and surfaces with a few papillae (S. limicola-scale). Three ctenidial cushions attached to the dorsal surface of notopodia appear on all segments except the 1st and 2nd segments which have two. Cirriform gills occur above the ctenidial cushions on all chaetigers from the 3rd. Ctenidia appear between the bases of dorsal tubercles and elytrophores. Ventral cirri present on all segments, and between the cirri and the body wall a small ctenidium occurs. Notopodia with numerous chaetae, a group of finger-like projections at the posterior base and terminal edge. Notopodial chaetae long spinose capillaries. Neuropodia extend as far as notopodia with a smooth bilobed posterior lobe and a sinuous row of chaetae. Neuropodial chaetae of three kinds: (1) a few simple unidentates with alternating rows of spines; (2) compound, with short blades, bidentate tips and smooth shafts; (3) compound with multi-articulate blades, bidentate tips and smooth shafts (S. limicola-detail).
Up to 100 mm for 200 chaetigers.
Sublittoral to the continental slope in sand and mud.
Atlantic between Canada and South Africa, Mediterranean, Adriatic, North Sea up to German Bight, Skagerrak, Kattegat, Öresund.