A scale-worm with a body of uniform width. Dorsal and ventral surfaces smooth.
Prostomium bilobed, with a peak on each lobe, a median antenna, a pair of lateral antennae, ventrally inserted, and a pair of palps. Two pairs of eyes, the anterior pair on the line of greatest width, the posterior pair near the rear margin.
First segment bearing chaetae and a pair of dorsal and ventral tentacular cirri. Scales overlap, covering the body. The first pair of scales are round, the rest oval to kidney-shaped, outer lateral margin fringed with a dense row of small papillae, with bulbous tips, posterior margin with sparse rows of similar papillae the surface covered with small tubercles, a row of very large stalked tubercles with rugose or flattened papillae on the upper surface, and a few scattered papillae (H. pagenstecheri-scale).
Notopodia are small mounds with a ventral acicular ligule and abundant chaetae. Notopodial chaetae spinose with blunt tips.
Neuropodia well developed with an anterior ligule and chaetae. Neuropodial chaetae spinose on the terminal quarter and with bidentate tips.
Up to 25 mm for 40 chaetigers.
Scales brownish sometimes with one or more dark patches. Surface tubercles often with halos of a pale colour in these patches.
Littoral to sublittoral.
English Channel, North Sea, western Scotland and off south-west Ireland.