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It is characterized by broad transverse brownish bands, alternating with thinner opaque white lines, the gills are mottled brownish.
It is most probably Marionia sp. 5 in IPN at page 339:
Gosliner, Terrence M., David W. Behrens & Ángel Valdés. 2008. Indo-Pacific Nudibranchs and Sea Slugs. Sea Challengers Natural History Books.
Gig Harbor, Washington. 426 pp.,
though IPN writes: "Body bright green with opaque white transverse lines and a network on the secondary gill bases. Light green gill respiratory branches, short but highly pinnate. There are 3-4 pairs of divided or simple velar tentacles."
Pretty similar or possibly the same species is:
Marionia sp. 18 Genus: Vayssière, 1877, which lacks brown spots on the sides of the body, and differs by solid brownish gills, and by brown spots forming transverse bands.
This species was posted on 16 September 2004 at these websites as Marionia sp. G Genus: Vayssière, 1877, and changed on 6 September 2011 into
Marionia sp. 07 Genus: Vayssière, 1877.
For some genera, such as Trinchesia was the alphabet almost through. I had to change the distinguishing alphabetic character into a number. I had chosen 2-digit numbers, even though '01' looks a little bit stupid, and now is only the genus italic written.
How to cite:
Köhler, E. (2016), published 8 March 2016, Marionia sp. 07 Genus: Vayssière, 1877
available from http://www.Philippine-Sea-Slugs.com/Nudibranchia/Dexiarchia/Marionia_sp_07.htm