Thorax cylindrical, abdomen tapering towards the pygidium.
Prostomium with three lobes and two eyespots. Tentacular filaments papillated.
Four pairs of long gills, divided in 2 branchial groups; groups well separated; gills of each group arranged more or less in one transverse row.
Collar chaetae fine and short, smaller than normal notopodial chaetae. Fourteen thoracic segments with notopodia with capillary chaetae, the posterior eleven also with neuropodia with uncini. Thoracic uncini with one row of 3-4 teeth abdominal uncini with 2-3 rows with ca. 8 teeth in each row. 15-18 uncinigerous abdominal segments (S. octocirrata-detail).
Posterior abdominal segments with a small cirrus at upper edge of each neuropodium.
Pygidium with two lateral cirri.
Up to 13 mm.
Narrow and cylindrical, thin layer of secretion encrusted with mud and usually attached to something hard.
In life body and buccal tentacles reddish yellow with the dark pulsating dorsal vessel visible through the body wall, gills pale green. In alcohol pale yellow.
On mud or sand or mixed bottoms; from upper sublittoral to a depth of 500 m.
Eastern North Atlantic to the Canary Islands, Mediterranean, South Africa, Canadian Atlantic. East Greenland, Iceland, the Faeroes, south and west Norwegian coast to Trondheimfjord, Skagerrak, Oslofjord, Swedish west coast, the Öresund, eastern Great Britain.