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I labeled it on 09 July 2012 Pseudocerotidae sp. 06, because my best guess was that it should be placed in the family Pseudocerotidae Lang, 1884,
I changed it on 11 July 2012 into Phrikoceros sp. 02 Genus: Newman & Cannon, 1996 because Juliana Bahia writes at the Marine Flatworms group of facebook: "Looks like a Phrikoceros..."
It looks pretty similar to the picture of Bulaceros porcellanus Newman and Cannon, 1996 in Gosliner et al., 1997 at page 97, except of the network of thin orange lines.
Gosliner, T.M., Behrens, D.W. & Williams, G.C. (1997) Coral Reef Animals of the Indo-Pacific. 314pp.
Monterey, California: Sea Challengers.