Onchidoris bilamellata (Linnaeus, 1767)

19 August, 2001.
Rubh Na Crannaig off the island of Eigg in the Inner Hebrides on the west coast. 
Water temperature 13° C. From 15 to 24 metres there were thousands of these small Dorids breeding and spawning on rock surfaces over a distance of 200 metres. How many more there must have been in the vicinity?
Nikonos 5 with 35 mm lens, 2:1 extension tubes and Ikelite 50 flash.