Thorunna sp. 3
Locality: Tablamu, 6 metres, Phangnga, Thailand, Andaman Sea, 27 February 2010, Rocky shoreline. Length: Approx. 8 mm. Photographer: Lawrence Neal.
From the orange mark on the front of the mantle this is most probably a species of Thorunna, but if so, it does not seem to fit any existing species - even allowing for a bit of variation. It could well be a juvenile, but even so it doesn't seem to fit.
Rudman, W.B., 2010 (March 29) Thorunna sp. 3 [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/thorsp3