(Linnaeus, 1767)
Description:
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 near the prostomial peaks, 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, about a quarter of the margins fringed with small papillae, the surfaces with small tubercles and sometimes a row of more distinct tubercles on the outer border.
Notopodia are small mounds with a ventral acicular ligule and abundant chaetae. Notopodial chaetae spinose with blunt tips.
Neuropodia well developed with an anterior acicular ligule and chaetae. Neuropodial chaetae spinose with bidentate tips, a few in upper and lower positions with unidentate tips
(H. imbricata-detail).
Size:
Up to 65 mm for 39 chaetigers.
Colour:
Variable, from yellow to black, with plain or patterned scales.
Habitat:
Littoral on rocky shores. Sublittoral to 230 m on varied bottoms. Sometimes found in tubes of other polychaetes. Has been recorded from brackish water in estuaries.
Distribution:
Northern hemispher; whole North Sea, Skagerrak, Kattegat, Öresund, Belts and Baltic Sea to southern Finland.