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Some scientists used to call the white colour form Tritoniopsilla alba, now known as Tritoniopsis alba, which has fewer of velar tentacles, and differs by pustules on the notum (smooth in T elegans) and lacks the opaque white markings on the notum.
Let me quote Wikipedia on the colour forms of Tritoniopsis elegans:
"The different colour forms do not seem to be a result of the animals' diet because the two forms sometimes occur alongside each other when the animals are feeding on the same colonial soft coral."
More information on Tritoniopsis elegans are on Bill Rudman's Sea-Slug Forum!
How to cite:
Köhler, E. (2017), published 7 March 2017, Tritoniopsis elegans (Audouin, 1826)
available from https://www.Philippine-Sea-Slugs.com/Nudibranchia/Cladobranchia/Tritoniopsis_elegans.htm