Polycera quadrilineata (Müller, 1776)

27 July, 2008.
Lephinchapel, Loch Fyne on the west coast. 
A mating pair at 14 metres.
Water temperature 12.5° C.
Fuji E900 camera in Ikelite housing, 2 x Inon D-2000 flashes and 2 x Inon CU lenses

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