Body cylindrical, posterior part of the abdomen tapering towards the pygidium. Prostomium broad, with three lobes, dorsally often concealed by a well-developed buccal segment.
Gills in two widely separated groups connected by a low dermal ridge; the three gills of each group free at the bases, but very close to each other and arranged in a triangle.
Chaetae of segment 3 small and fine, shorter than or not much longer than the notopodial chaetae, 15-20 on each side. Twelve segments with long notopodial capillary chaetae; notopodia of last thoracic segment elevated with left and right chaetae of this segment with frayed tips, usually crossing middorsally; laterally the 12th notopodia bear a more or less prominent hump. Nine thoracic and 12 abdominal uncinigerous segments. Uncini very small, pectinate, with more than 3 vertical rows of 4-5 teeth (M. wahrbergi-chaetae). Pygidium with two slender cirri and 4 small red eyespots.
Up to 4.3 mm.
In alcohol pale yellow.
Very few records, from areas with mud and mixed bottoms and depths of 20-80 m.
Oslofjord, Agder, Swedish west coast, Jutland, Skagerrak, Kattegat.