Body long, thin and cylindrical.
Prostomium oval, longer than wide, with an encircling rim, higher anteriorly, laterally and posteriorly not incised. Nuchal slits almost extending to the whole head, straight and slightly diverging anteriorly. Without ocelli.
27 chaetigers. The eight anterior chaetiges with more or less complete glandular band on the anterior part of the segment; other segments with glands around the parapodia.
Notopodial capillary chaetae winged or without wings, sometimes with a feathery tip.
Neuropodial chaetae on the three anterior chaetigers are reduced hooks. Oher hooks are more curved with one large tooth and seven rows of small teeth and a tuft of hairs.
Only the last posterior segment without chaetae. (M. acirrata-chaetae).
Pygidium conical, with longitudinal fold, without cirri.
Up to 55 mm for 27 chaetigers.
Covered with fine sand. Diameter outside 1 mm.
Chaetigers 4-8 more or less spotted red, especially dorsally.
North Pacific, western Norway up to Skagerrak and Kattegat.