Body slender, anteriorly and posteriorly tapered.
Prostomium rounded, conical, longer than broad. Eyes medium-sized, red, situated near the posterior margin of the prostomium. Median antenna very small, papilliform and situated just anterior to the eyes. Proboscis covered with conical papillae. Terminal ring of 6 big and 6 small papillae (P. spinachia-proboscis). Dorsal tentacular cirri of segment 2 reaching about segment 4; ventral tentacular cirri oval, flattened, somewhat bigger than the ventral cirri, with a ventral ciliary band. Dorsal cirri oval, one and a half to two times as long as broad. Ventral cirri similar to dorsal cirri but smaller (P. spinachia-parapodium). Terminal end of chaetal shaft with many teeth, decreasing in size proximally. Blades of medium length.
Pygidial cirri oval to finger-like (P. spinachia).
Up to 12 mm long for 75 segments.
Living animals transparent whitish to yellowish, with many dark green spots.
Northern North Sea to northern Öresund, Mediterranean.