Body slender and fragile.
Prostomium with four eyes in a trapezoid arrangement and two ocelli. Palps about as long as the prostomium, divergent although fused at the base. Median antenna almost three times as long as the prostomium, inserted somewhat in front of the lateral antennae. Lateral antennae longer than prostomium. Dorsal tentacular cirri about as long as the lateral antennae; ventral tentacular cirri shorter. Dorsal cirri of the first parapodium almost twice as long as the dorsal tentacular cirri, the other dorsal cirri mostly shorter than the width of the segments. Ventral cirri of the first parapodium broadly leaf-like, the others small. Antennae and cirri are smooth.
All parapodia with one acicula. Anterior aciculae with a terminal button and distally weakly incised. Blades of compound chaetae long or short, bidentate. Posterior parapodia also with two simple chaetae: a capillary and a thicker, weakly bent chaeta.
Pharynx with a smooth or slightly irregular edge, surrounded by 10 soft papillae and bearing a single tooth anteriorly. Proventriculus short with 22-25 rows of glands.
Body up to 7 mm long for 60 segments.
Transparent or dorsally with dorsolateral and median cross-line with purple or blackish shade.
At low water, in tide-pools and in the shallow sublittoral, in kelp holdfast and amongst ascidians.
North Atlantic to Mediterranean, English Channel to southern North Sea.