(Delle Chiaje, 1828)
Body relatively slim and firm. Tentacles numerous, long, thick. Upper lip low, covering the mouth dorsally and laterally. Buccal segment ventrally forming a narrow brim. Many eyespots. Gills dichotomous with short stems and very short tips, more or less flattened, diminishing in size from the first to the third pair. Lateral lobes on segments 2-4. Ventral shields on 15 thoracic segments. Notopodial chaetae from segment 4. Seventeen chaetigerous thoracic segments. Uncinigerous tori from segment 5. Uncini in double rows on segments 11-20. Pygidium with fringed edge. Notopodial chaetae smooth with relatively broad brims. Uncini with one big and several smaller teeth.
Up to 60 mm for 90 segments.
Thin, fragile, encrusted with sand, often fastened to large solid objects.
In life reddish brown, dark brown, dark orange, yellowish green, or olive; tentacles yellowish, gills red. In alcohol yellowish.
On silt, sand and mixed bottoms, or among Laminaria rhizoids; eulittoral to about 300 m; euhaline and at least transitory in polyhaline conditions.
Eastern North Atlantic to Senegal, Mediterranean, Canadian Atlantic, Japan, California; Jan Mayen, Iceland, the Faeroes, Shetland, entire Norwegian coast, Kattegat, the Öresund.