Onchidoris bilamellata (Linnaeus, 1767)

March 2000.
Dunollie Point, Oban on the west coast.
Around 12 to 14 metres there were many of these common little animals, each approx 23 mm long.
There were several groups made up of two, three, four and more piled up on top of one another and amongst their spawn. There were many single animals crawing about the gritty sand surface. Spawn was found in the vicinity on the upper surface of small rocks. Deeper down (26 metres) several animals were noted among barnacles and the remains of barnacles.

for more information about this species go to one of the links below
OPK - Opistobranquis

nudibranchs of the british isles sea slug forum