Body with a central disc of up to 15 mm in diameter and 5 short, straight arms of about 4 times that length; coloured reddish brown with conspicuous white radial shields.
The scales on the disc are rather coarse. The primary plates are not very distinct. The radial shields are small, but conspicuous due to their white colour. Outer arm combs with 10-12 short papillae; inner arm combs small and indistinct (O. albida disc).
The dorsal and ventral arm plates have a convex outer edge. The innermost dorsal arm plates are heart-shaped. There are 3 pairs of arm spines per segment. The tube foot pores with only 1 tentacle scale, except for the proximal 3-5 pore pairs which usually have 2-3 tentacle scales (O. albida arm).
The mouth shield is short, about half of the disc radius. There is a single vertical row of teeth on top of the jaw, and 3-5 simple mouth papillae on each side of the jaw (O. albida mouth).
It is found at a variety of soft substrata, from about 4 to 850 m.
In the North Sea this species is found on all coasts. Elsewhere it is distributed in the north-east Atlantic from Norway to the Azores, and in the Mediterranean.