(Grube, 1840)
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 on the line of greatest width, the posterior pair in front of the rear margin.
First segment bearing chaetae and a pair of dorsal and ventral tentacular cirri. Scales overlap, but leave some posterior segments exposed. The first pair of scales are round, the rest vary from oval to kidney-shaped, the margins with very short papillae on less than a quarter of the circumference, the surfaces with small tubercles and a row of larger tubercles on the outer border.
Notopodia are small mounds with a ventral acicular ligule and numerous chaetae. Notopodial chaetae spinose with blunt tips.
Neuropodia well developed with an anterior acicular ligule and numerous chaetae. Neuropodial chaetae of 2 kinds: 1) spinose with bidentate tips; 2) a few upper and lower chaetae spinose with unidentate tips (H. extenuata-detail).
Size:
Up to 70 mm for 47 chaetigers.
Colour:
Variable, from grey to red, with plain or patterned scales.
Habitat:
Littoral on rocky shores, to 1250 m on varied bottoms. Sometimes found in the tubes of other polychaetes.
Distribution:
Arctic, North Pacific, North Atlantic up to the Mediterranean, Adriatic, Black Sea, English Channel, probably whole North Sea, Skagerrak, Kattegat, Öresund. South Africa.