Click the thumbnail photos to enhance!
It is probably Elysia sp. 10 in
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 83
Maybe it is the same species as Elysia sp. 14, which does not stretch its parapodia.
It was originally posted at these websites as Elysia sp. C Genus: Risso, 1818.
For some genera, such as Trinchesia is 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.