(M. Sars, 1872)
A small, cylindrical body.
Prostomium oval, a little longer than wide. Nuchal slits parallel and extending to the anterior half of the head.
23 chaetigers. 4th chaetiger without collar. The first eight chaetigers with glandular bands anteriorly, on chaetigers 4-8 glandular areas may be present on posterior parts. On the rest of the body glands present only on parapodia.
Notopodial chaetae are all winged capillaries, some with feathery tips.
Anterior 3 segments with ventral spines, following segments with hooks except 1 or 2 posterior segments in which chaetae are absent (I. planiceps-detail).
Pygidium funnel-shaped, with 20 equally short and almost triangular cirri.
Up to 40-70 mm for 23 chaetigers.
Straight, cylindrical, covered with mud, fine sand or foraminiferans and plant material. Diameter outside 3.5-4 mm, inside about 2 mm.
In formaldehyde yellowish-brown, especially on the posterior half of the anterior segments.
North Pacific, North Atlantic, western Norway, Skagerrak, Kattegat.