Tentacles 0.9-1.2 mm long. Two relatively large so-called statocysts in front of eyes between the tentacles. Two reddish-brown pigmented eyes between the tentacles (often lacking in specimens from the Baltic Sea population). Nuchal organs oval, directly behind tentacle bases. Ciliation comprised of small tufts and sensory cilia on head and trunk segments. Extension of the salivary glands variable, up to segment 16 or 17. Two pygidial lobes broad, rounded, highly variable in shape.
Fertile region in the males begins in segment 10, in the females usually in segments 12-15. Lateral organs from segment 7 to 11 in the males. One pair of spermioducts in segment 10. Oviducts in two posterior segments. Unpaired dorsal organs in females usually from segment 17 (also from segments 16, 18, 19 and 20) backwards, somewhat in front of middle of segment.
Up 15 mm for 71 segments.
Creamy-white, transparent except for individuals that have passed the reproductive period and then appear rather opaque. Pharynx region red.
Coarse and gravelly sand in the upper shallow subtidal and in the surf zone.
North Sea (southern Scotland to Northumberland), Limfjord (Denmark), Irish Sea, Skagerrak (west coast of Sweden, Gullmarfjord), Atlantic (west coast of Norway, Hardanger, Tromsö), Baltic Sea (Bay of Kiel).