Body short, posterior part of abdomen tapering towards pygidium.
Prostomium without glandular ridges or eyespots. Buccal segment ventrally long, with longitudinal folds.
Three pairs of gills united by a membrane. Gills in two groups, well separated and connected by a low membrane; the three gills of each group in a transverse row. Segment 3 achaetous. Seventeen thoracic segments with notopodia with capillary chaetae, the posterior fourteen also with neuropodia with uncini. Thirteen abdominal uncinigerous segments. Uncini with 2-3 rows of teeth with 4-8 teeth in each row (S. sexcirrata-detail).
Pygidium with round papillae.
Up to 25 mm.
In alcohol pale yellow or whitish.
Mainly on mud, occasionally on mixed bottoms; upper sublittoral to about 5000 m.
Canadian Atlantic, Arctic, North American Pacific (California). Svalbard, Norwegian Sea, Shetland, Norwegian coast, North Sea, Skagerrak, Kattegat, Swedish west coast, north coast of Jutland.