Body cylindrical and strong.
Prostomium clearly longer than wide, with a raised median keel. Rim with a notched margin. Nuchal slits are short, anteriorly slightly diverging.
19 chaetigers. First chaetiger enlarged into a collar.
Chaetigers are about as long as broad.
A complete glandular band present on peristomium and three first chaetigers. On other parapodia small glandular patches ventrally.
Notopodia are small, bud-like, neuropodia are tori.
Three kinds of capillary chaetae: 1) strongly bent with smooth wings 2) straight, narrow and with smooth wings 3) long, thin, finely denticulate.
Ventral hooked chaetae present from 2nd anterior segment.
Two posterior segments without chaetae (M. sarsi-chaetae).
Pygidium with an oval to rounded plate, the dorsal edge rounded, the ventral edge smooth, wavy or jagged.
Up to 110 mm for 19 chaetigers.
Cylindrical with a circular cross-section. Covered with mud, fine sand or foraminiferans. Diameter outside 3 mm, inside 1 mm.
Anterior body with brown to black-brown irregular pigment stains. Posterior body half yellowish-grey.
From upper sublittoral, 8 m down to 4400 m deep.
Cosmopolitan. North Sea, Skagerrak, Kattegat up to middle Öresund and Big Belt.