Polycera quadrilineata (Müller, 1776)

6 July, 2008.
Skelly's Holes, St Abbs on the east coast. 
A pair at 10 metres; there were many animals 10 - 18 mm throughout the dive.
Water temperature 11° 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