A scale-worm with a bidy of uniform width. Dorsal and ventral surfaces smooth.
Prostomium bilobed, with distinct peaks on each lobe, a papillated median antenna, a pair of lateral antennae, ventrally inserted, and a pair of palps. Two pairs of eyes, the anterior pair below the prostomial peaks, the posterior pair in front of the rear margin.
First segment bearing chaetae and a pair of finely papillated dorsal and ventral tentacular cirri.
Scales overlap, covering the body. The first pair of scales are round, the rest oval to kidney-shaped, the margins smooth or with occasional short papillae, the surfaces with a patch of small tubercles. Notopodia are small mounds with a ventral acicular ligule and abundant chaetae. Notopodial chaetae are stout and spinose with blunt cleft tips. Neuropodia well developed with an anterior acicular ligule. Neuropodial chaetae spinose with bidentate tips (H. spinifera-detail).
Up to 15 mm for 39 chaetigers.
Scales brown to black.
Littoral and sublittoral, in Laminaria holdfasts and from burrows of Perinereis cultrifera and Nereis irrorata .
Northern Spain and the Mediterranean, western English Channel, Irish Sea, western Ireland, Shetland.