Body thread-like; its surface characteristically wrinkled. Segment borders recognizable only by slight constrictions; segment 1 shorter than the following. Tentacles at least reach level of the pharyngeal bulb if extended posteriorly. Specific pattern of dorsal ciliation on preoral part of prostomium. Ventrally with cilia on nearly entire area in front of mouth; midventral ciliary band, on all but last 4 or 5 segments. Segments 2 to last with two pairs of chaetae and a pair of tufts of sensory cilia. Chaetae 35-40 µm long, sigmoid and bifid as in tubificid oligochaetes, emerging somewhat posteriorly to middle of segment. Sensory cilia on a small dorsolateral papilla on each side of segments 1 to last always posterior to chaetae, except on achaetous segment 1. Pygidial lobes rounded and relatively large, but only slightly wider than most posterior part of trunk; with subterminal band of ventral adhesive gland openings.
Fertile region from segment 20 or so backwards. Females with 4-17 oocytes at a time. Males with spermioducts in each fertile segment, with lateral openings somewhat in front of chaetae of following segment.
Up to 13 mm long for up to 50 segments, usually smaller (6-8 mm), especially when contracted.
Transparent, with light yellowish, greenish or completely colourless refringent glands and four other types of epidermal glands, partly accumulated in longitudinal bands.
Medium and coarse, rarely fine, sand. Sublittoral, mostly middle and lower parts of intertidal areas, especially water-saturated coarse sandflats. Occurs in salinities of down to near 18 ä.
North Sea, English Channel, French Atlantic coast (Arcachon), Irish Sea, Baltic Sea, West Greenland, Mediterranean, Atlantic and Pacific coast of North America, Indian Ocean, South Africa.