A scale-worm with a body of uniform width. Dorsal and ventral surfaces smooth.
Prostomium bilobed, without peaks (sometimes the margin to the outside of the lateral antennae appears like a peak), with a median antenna, a pair of lateral antennae, laterally inserted, and a pair of palps. Two pairs of eyes, the anterior pair near the anterior border, the posterior pair near the rear margin.
First segment bearing chaetae and a pair of dorsal and ventral tentacular cirri. Scales overlap, almost covering the body. The first pair of scales are round, the rest oval to kidney-shaped, the margins with a few small papillae on the outer lateral edge, the surfaces with numerous small tubercles and a few papillae.
Notopodia are small mounds with a ventral acicular ligule and numerous chaetae.
Notopodial chaetae with spinose and blunt, usually cleft, tips.
Neuropodia well developed with an anterior acicular ligule and abundant chaetae.
Neuropodial chaetae of 3 kinds: 1) upper group, capillaries with rows of spines; 2) median group, with rows of spines and bidentate tips; 3) lower group, a few short, curved spinose chaetae with unidentate tips (M. glabra-detail).
Up to 25 mm for 38 chaetigers.
Brownish marks on scales.
Littoral to sublittoral on sandy mud, recorded in tubes of Chaetopterus variopedatus and burrows of Neoamphitrite edwardsi .
Arctic, North Atlantic, English Channel, probably whole North Sea, Skagerrak, Kattegat and Öresund.