Body of this scale-worm is oblong, tapering more posteriorly than anteriorly.
Prostomium bilobed, wider than long, with distinct peaks. Two pairs of eyes, anterior pair largest, lateral, slightly anterior to greatest width of prostomium, posterior pair dorsal, near posterior margin. Median antenna 3-5 times longer than prostomium with long, bulbous basal joint extending far beyond prostomial peaks. Lateral antennae 1/3-2/3 length of prostomium with basal joints extending slightly beyond prostomial peaks and inserted ventrally. Antennae covered with short papillae. Palps long, 3-4 times length of prostomium, tapering, with longitudinal rows of small papillae.
First segment with cirrophores directed anteriorly, lateral to prostomium, each with acicula, 0-3 chaetae and pair of tentacular cirri similar to median antenna, but a little shorter.
Scales oval to kidney-shaped, completely covering dorsum, usually with fringe of short papillae on lateral and posterior border edge, but sometimes lacking on posterior scales. Surface of scales with numerous microtubercles, conical, distally blunt to slightly curved, without macrotubercles.
Notopodium rounded, extending into acicular lobe. Neuropodium tapering distally to thick acicular process. Notopodial chaetae numerous, moderately stout, slightly thicker than neuropodial chaetae, with long spinose regions and sharp to blunt bare tips. Neuropodial chaetae numerous, with short, spinose regions and bare tips, usually with small, narrow secondary tooth.
Dorsal cirri on segments without scales similar to tentacular cirri, but a little smaller. Ventral cirri shorter, with few papillae (H. viridis-detail).
Up to 38 mm for 41 segments.
Living animal totally green, in ethanol pale yellow or brownish; scales pale yellow with brown spots.
Usually on hard bottoms with stone, sand and shell, but also on soft bottoms with mud and clay. 30-120 m deep.
Along the coast of Norway and SW Sweden.