Body long and slender.
Prostomium anteriorly broadly rounded with anterior corners usually flared, forming short frontal horns, with or without four eyes, without antenna. Caruncle double, reaching chaetiger 3. Two relatively short palps, reaching no further than the 10th segment.
Notopodial postchaetal lobes in anterior segments, long, cirriform, basally fused to the gills, becoming shorter posteriorly.
Neuropodial postchaetal lobes in anterior segments oval, becoming shorter posteriorly.
All parapodia with winged capillary chaetae. Neuropodial hooks start at chaetiger 11-52, the notopodial hooks 1-12 chaetigers later.
Gills start at chaetiger 1, up to 65 pairs, gradually disappearing in mid-body segments (M. viridis-parapodium).
Pygidium with up to 14 filamentous cirri.
Up to 115 mm for 250 segments.
Darss-Zingst Bodden, Greifswalder Bodden, Elbe estuary. Originally from North America.