Body cilindrical somewhat attenuating towards the end, up to 500 mm in length; coloured dark brown.
There are 10 thick, bushy, almost black tentacles.
Tube-feet are completely retractile, arranged in numerous series, spreading to some degree also over the interradii on the dorsal side.
Skin very thick and leathery. Younger specimens with variable numbers of larger fenestrated plates and a few small tubercles in younger specimens; older specimens almost completely devoid of calcareous deposits (C. frondosa spicules).
This species lives on hard substrata and kelps, from about 0-200 m.
In the North Sea this species is known from the Shetland Islands and the Orkney Islands. Elsewhere widely distributed over the Arctic region.