Body slender and fragile.
Prostomium semicircular with two red eyes, placed near the posterior edge of the prostomium. Prostomium with 3 antennae and 2 simple palps.
Median antenna as long as lateral ones, inserted at the posterior edge of the prostomium. Lateral antennae as long as prostomium. Palps at most half the length of the prostomium. 6 pairs of simple tentacular cirri on 3 segments.
Dorsal tentacular cirri of second segment the longest, almost twice as long as the median antenna. Dorsal and ventral cirri simple.
Dorsal cirri often longer than longest tentacular cirri. Ventral cirri a little longer than the parapodial lobes.
Blades of compound chaetae on all parapodia of different sizes, finely serrated and bidentate. Simple chaetae present in upper and lower neuropodia, serrated at one side and with bidentate tips (M. sezelkowii-detail).
Pygidial plate broadly rounded, with a smooth edge and occasionally with a weak median notch. Pharynx with 10 terminal papillae, without jaws.
Body up to 7 mm for 27 segments.
Body yellowish to whitish with 4 brownish cross-lines on each segment, interrupted by lateral pigmentation.
Interstitial in sand, also on tidal flats beneath stones and in Arenicola burrows. Eulittoral to upper sublittoral.
North Atlantic, English Channel, North Sea, Skagerrak.