Photos by Guido Zsilavecz
This nudibranch is fairly wide-spread, occuring as far north as Ireland, and along the coasts of England, France, Spain, and probably further down south. It is always associated with gorgonias of the genus Eunicella, such as our common sinuous sea fan, Eunicella tricoronata. As can be seen from the photos, it so resembles the sea fan that it is extremely hard to see, which is probably why it has escaped Peter's and my attention for so long. Only when we removed the animal and placed it next to the sea fan could we see it properly ourselves!
The eggs are a slender string wound around a branch of the fan, as can be seen in the bottom-most image.
Nudibranchs of Southern Africa - a guide to the opisthobranch molluscs of southern Africa, T Gosliner, 1987.
A Field Guide to the Nudibranchs of the British Isles, B Picton and C Morrow, 1994.