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This specimen was identified by Dr. Richard Willan, thanks!
It is Goniodoridella sp. 4 in IPN:
Gosliner, Terrence M., David W. Behrens & Ángel Valdés. 2008. Indo-Pacific Nudibranchs and Sea Slugs. Sea Challengers Natural History Books.
Gig Harbor, Washington. 426pp. at page 127.
It was posted at these websites before as Goniodoridella sp. B Genus: Pruvot-Fol, 1933.
For some genera, such as Trinchesia was the alphabet almost through. I had to change the distinguishing alphabetic character into a number. I have chosen 2-digit numbers, even though '01' looks a little bit stupid, and now is only the genus italic written.