Body small with up to 42 segments. Appendages are easily lost.
Prostomium trapezoid, broader than long, with four eyes in a trapezoid arrangement and two ocelli at the base of the lateral tentacles. Palps very short dorsally hardly visible. Median antenna longer than lateral ones. Lateral antennae, club-shaped, a little longer than prostomium.
Prostomium and peristomium clearly separated. Peristomium shorter than the following segments.
Tentacles, tentacular cirri and usually dorsal cirri smooth. Dorsal cirri may be faintly annulated. Ventral cirri weakly annulated.
Two pairs of tentacular cirri. Tentacular cirri about as long as the segments width.
Dorsal cirri finger-like, longer than the width of the segments. Ventral cirri much longer than parapodial lobes (S. websteri-parapodia).
First parapodium with a thin, distally buttoned acicula. Parapodia 2-5 with very thick, buttoned acicula. Following aciculae thinner.
In the first 6 parapodia, blades of compound chaetae thicker than the following (S. websteri-chaetae). All parapodia with a simple chaeta equipped with a delicate hood, fine teeth along the blade and some strong teeth at the tip.
Pharynx without teeth.
Pygidium with 3 cirri, median the longest.
Body up to 5 mm long for 42 segments.
Transparent, gills with yellowish granulae, pharynx reddish brown.
From mid-eulittoral down to about 80 m deep, on sandy bottoms.
North-east Atlantic, South-west Indian Ocean, English Channel, North Sea.
This species is possibly identical to the insufficiently known species Streptosyllis arenae .