Family Plakobranchidae

This example of the Order Sacoglossa - basically sapsuckers - is most likely Elysia sp

On a night dive there were hundreds of these creatures generally feeding on Tydemania expeditionis under Andulus Marina in Sharm Obhur north of Jeddah.

Average size would be around 20mm and this particular shot was taken using a Nikon F3 with Nikkor 60mm micro lens using Fuji Velvia.