Body cylindrical, broad and flattened anteriorly.
Prostomium triangular, with frontal horns anteriorly and a broad, short caruncle posteriorly. With or without four eyes, without a median antenna. The long palps may reach segment 10, often lost.
Notopodial postchaetal lobes cirriform, connected by a ciliary band from the 3rd or 4th segment onwards.
Neuropodial postchaetal lobes on anterior four segments large, triangular, on the following segments smaller and broadly rounded.
First neuropodium with 1-3 big, strongly bent spines. All parapodia with capillary chaetae. From neuropodium 15-16 also bidentate hooded hooks and a strongly bent spine present. Segment 5-15 with more or less developed glandular areas with thin tapering glandular chaetae (S. bombyx-chaetae).
Pygidium with two filamentous cirri.
Up to 60 mm for 180 segments.
Anteriorly pink, wine-red or green posteriorly.
On sand rarely on muddy or mixed sediments, eulittoral to 1000 m. Live in Y-shaped tubes, encrusted with sand. Tubes 2 mm in diameter and 25 cm long.
Arctic, North Pacific, North Atlantic to Mediterranean, whole North Sea to Öresund, English Channel, South Atlantic, South Pacific to Subantarctic.