(M. Sars, 1872)
A scale-worm with broad, flat body of 43 segments.
Prostomium somewhat broader than long, bilobed, with a peak on each lobe. Median antenna long, lateral antennae small, papillate. Palps long and pointed, with tiny papillae. Two pairs of eyes, the anterior pair near the line of greatest width, the posterior pair in front of the rear margin. Tentacular cirri similar to median antenna. First segment with aciculae and four chaetae.
16 pairs of thin scales. The first pair of scales are round, the remainder kidney-shaped, margins fringed with papillae, the surfaces smooth, with a few papillae and microtubercles on the anterior part.
Notopodial chaetae are thick and long with rows of spines and pointed tips. Neuropodia well developed with an anterodorsal ligule and chaetae in rows. Neuropodial chaetae uni- and bidentate, with rows of spines; the distal spines enlarged, forming a brush-like tip (A. mollis-detail).
Up to 50 mm for 43 chaetigers.
Dorsum with dark transverse banding.
North Atlantic to Skagerrak.