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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,
Phyllidia exquisita which has a pale bluish granular background colour, black swirls, and yellowish-orange pigment at the mantle margin
Phyllidia willani which has longitudinal black swirls an a white granular appearance, and lacks orange pigment at the mantle margin
Phyllidia sp. 01 which has a pale yellowish-orange background colour, and lacks the black rings
I can't tell for sure how to distiguish the phyllidiids with the whitish 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 babai are on Bill Rudman's Sea-Slug Forum!