Body slender, anteriorly and posteriorly tapered. Prostomium triangular, longer than broad. Median antenna minute, often deeply sunk and difficult to see, situated slightly in front of eyes. Eyes small, oval. Proboscis long and thin, covered with diffusely distributed rounded papillae. Tentacular cirri of segment 1 shorter than segment width. Dorsal tentacular cirri of segments 2 and 3 reaching segments 4-5. Ventral tentacular cirri short and slightly flattened, provided with small parapodial lobes fused to the cirrophores, carrying about five chaetae. Dorsal cirri of median segments inflated, oval. Parapodial lobes asymmetrical, the upper part slightly larger than the lower part, carrying about ten compound chaetae. Terminal end of chaetal shaft with a large, slightly bent tooth and a number of smaller ones on each side, decreasing in size proximally. Blades long and slender. Capillaries may occur on posterior segments. Ventral cirri slightly more pointed and smaller than dorsal. Pygidial cirri distally tapered, 4-5 times as long as wide. Median pygidial papilla present. Single bands of cilia ventrally on posterior segments.
Up to 40 mm for 185 segments.
Living animals with a yellowish ground-colour, more or less densely covered with green pigment spots, giving the animals a dark and rich emerald-green hue. Pigment spots especially dense on dorsal and ventral cirri. Eyes clear red. Preserved animals yellowish to dark brown, eyes brownish.
Rocky bottoms or shell gravel and sand, from 15 to 80 m depth.
North Atlantic, Mediterranean, English Channel, northern North Sea up to Skagerrak.