Polycera quadrilineata (Müller, 1776)

4 October, 2009.
Cave, Hyskeir on the west coast. 
20 mm animal, one of several, at 16 metres. Water temperature 13° C.
Fuji E900 camera in Ikelite housing, 2 x Inon CU lenses and 2 x Inon D-2000 flashes.

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