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Gosliner, T.M., Behrens, D.W. & Williams, G.C. (1997) Coral Reef Animals of the Indo-Pacific. 314pp.
Monterey, California: Sea Challengers.
It looks also similar to the "White flatworm" at the Wild Singapore website, and to Pseudobiceros cf. confusus on the South-west Indian Ocean Flatworm site.
I label it Pseudocerotidae sp. 01 because the similar species are in different genera in the family Pseudocerotidae Lang, 1884.