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This species is Janolus sp. 2 in IPN at page 318:
Gosliner, Terrence M., David W. Behrens & Ángel Valdés. 2008. Indo-Pacific Nudibranchs and Sea Slugs. Sea Challengers Natural History Books.
Gig Harbor, Washington. 426pp.
The cerata and the rhinophores are pale yellowish/cream with a purple apex merging into bright blue. The caruncle is also pale yellowish/cream.
Pretty similar are:
Janolus sp. 01 which differs by the rhinophores: brown with white tips, and the cerata: yellow subapical ring
Janolus sp. 03 which has opaque white specks on the cerata and rhinophores
Janolus sp. 05 which differs by the rhinophores: blueish tinge with darker apices, and by the cerata: translucent with a diffuse yellowish ring below the purple ring
It was originally posted at these websites as Janolus sp. B Genus: Bergh, 1884.
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.