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Pretty similar are:
Phyllidia ocellata which is very variable in colour, but has usually a yellow-orange ground colour of the mantle, and has large black rings,
Phyllidia babai which lacks the longitudinal black swirls, it has black rings
Phyllidia exquisita which has a pale bluish granular background colour, black swirls, and yellowish-orange pigment at the mantle margin
Phyllidia sp. 01 which has a pale yellowish-orange background colour
These two specimens which I identified as Phyllidia willani #1 and #2 have both some orange pigment anteriorly at the mantle margin, they might be Phyllidia exquisita.
I can't tell for sure how to distiguish the phyllidiids with the whitish/bluish granular appearance:
Phyllidia babai, Phyllidia exquisita, Phyllidia willani, Phyllidia sp. 01 and Phyllidia sp. 3 in IPN at page 292. I guess they are variants of one species.
Bill Rudman thinks Phyllidia babai, Phyllidia exquisita, and Phyllidia willani to be variants of the very variable Phyllidia ocellata.
More information on Phyllidia willani are on Bill Rudman's Sea-Slug Forum!
How to cite:
Köhler, E. (2017), published 30 July 2017, Phyllidia willani Brunckhorst, 1993
available from https://www.Philippine-Sea-Slugs.com/Nudibranchia/Doridina/Phyllidia_willani.htm