Column elongated, not divided into distinct regions, its aboral end rounded and provided with cinclides; periderm is absent. Disc small, with a slight hypostome; tentacles very long - even in contraction being much longer than the disc diameter - in extension tapering to fine points. Length of column when not buried up to 100 mm, becoming much longer when buried; full expanse of tentacles up to 100 mm.
Colouration: Colour of column dirty white or flesh-colour, sometimes suffused with vivid green on the mesenteric insertions, usually with a white streak on each macrocoele at the distal end. Disc and tentacles translucent grey-brown, disc with reddish lines on the mesenteric insertions and often with small white spots on the exocoels, close to the mouth; lips and actinopharynx may be vivid green. Tentacles often shading to reddish-brown distally, each one having a more or less extensive white spot near its base. Specimens from localities outside Britain may be more or less suffused with pink or red on the column, disc and tentacles.
Burrows in mud, sand, or gravel, always offshore, occurring down to at least 1000 m.
In Britain known only from south-west and west Ireland, at 10-25 m. Elsewhere this species has an unusually wide distribution, occurring in the cold temperate and sub-polar regions of both hemispheres; it has been recorded in all western European seas, including the Mediterranean.