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It looks pretty similar to Gymnodoris alba which differs by the gills, which form an incomplete circle around the anus.
This species is most likely as Gymnodoris sp. 17 in IPN at page 153.
Gosliner, Terrence M., David W. Behrens & Ángel Valdés. 2008. Indo-Pacific Nudibranchs and Sea Slugs.
Sea Challengers Natural History Books. Gig Harbor, Washington. 426pp.
How to cite:
Köhler, E. (2017), published 29 May 2017, Gymnodoris sp. 01 Genus: Stimpson, 1855
available from https://www.Philippine-Sea-Slugs.com/Nudibranchia/Euctenidiacea/Gymnodoris_sp_01.htm