(Forbes & Goodsir, 1867)
Description
Body cilindrical, up to 40 mm in length; coloured white or brownish.
Tentacles
There are 10, sparsely branched, white tentacles.
Tube-feet
The tube-feet are scarce, not quite contractile and arranged in 5 zigzag rows.
Skin
The skin is very thick, leathery and smooth, with numerous calcareous deposits consisting of (1) plates with usually 4 holes and many nodules, or (2) large, more irregular plates, and (3) small irregular star-shaped cups in the outer layers of the skin (O. lactea spicules).
Habitat
This epifaunal species is found on hard substrata, where it lives among shells, calcareous algae, and other sessile animals; from shallow water down to depths of 100 m.
Distribution
In the North Sea this species is known from the Shetland Islands down to Northumberland and Durham on the British east coast. Elsewhere it is distributed from Norway to Brittany.
Remark
This species has been confused with the small form of Ocnus planci.