Height and diameter of base up to 100 mm.
Base normal, forming an adherent disc (cf. Actinauge). Column divided into scapus and scapulus, the scapus with more or less well-developed solid tubercles. These are variable in size and occurrence, usually tending to form longitudinal rows ending at the junction with the scapulus in a ring of 12 large coronal tubercles; sometimes, usually in young specimens, only the coronal tubercles are present or these too may be absent. Periderm is usually present but often only in patches. Scapulus with 12 longitudinal ridges originating from the coronal tubercles.
Tentacles: Moderate or long in extension, arranged hexamerously in five cycles, up to 96.
Colouration: Colour of column whitish, buff, orange or reddish, with the scapular ridges often dark. Disc whitish or purplish, sometimes with a pattern of dark brown spots, tentacles pale brown to deep purple.
Reproduction: Viviparity has been recorded on one occasion.
Typically on shells, particularly those of the large whelks Buccinum and Neptunea but also on other species, living or dead; sometimes on shells containing hermit crabs (Pagurus bernhardus). An offshore species occurring usually on sandy bottoms from about 20 to 200 m depth.
It has been found on the North Sea coasts of England and Scotland, in northernmost Europe-Greenland, Spitzbergen, Scandinavia, etc.