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I thought at first sight: "This is a flatworm!" Often people are fooled by flatworms of the genus Callioplana because these species have similar looking simple thin 'rhinophores', located exactly the same.
Then sent Gordon Tillen the picture with the vertral view which shows a foot, absent in all kinds of flatworms, so it must be some kind of dorid with retracted gills. How about the rhinophores? I know only one species with thin simple rhinophores: Doridomorpha gardineri, which looks completely different! My next guess was: the rhinophores are retracted, only their tips are visible..., at least the tips of the rhinophores are tan.
I place it in the family Discodorididae because of the general shape of the body, but this is also only a guess!
How to cite:
Köhler, E. (2017), published 21 March 2017, Discodorididae sp. 09 Family: Bergh, 1891
available from https://www.Philippine-Sea-Slugs.com/Nudibranchia/Euctenidiacea/Discodorididae_sp_09.htm