Adalaria proxima (Alder & Hancock, 1854)

January 2000, Loch Fyne at Lephinchapel Reef.
There were several of these 10mm long animals on the kelp fronds at 4-5 metres.

for more information about this species go to one of the links below
OPK - Opistobranquis nudibranchs of the british isles sea slug forum