Click the thumbnail photos to enhance!
it is as Pseudoceros sp. 6 at page 110 in
Gosliner, T.M., Behrens, D.W. & Williams, G.C. (1997) Coral Reef Animals of the Indo-Pacific. 314pp.
Monterey, California: Sea Challengers.
This species is very variable, as the 21 pictures at NUDIPIXEL are demonstrating.
Let me quote Marcela Bolanos at LifeDesks:
"Cream yellowish background fading to white towards the margin with irregular black maculae on either side of the median line and an orange marginal band."
This specimen might be as well a variant of Pseudoceros scintillatus
How to cite:
Köhler, E. (2017), published 17 September 2017, Pseudoceros scriptus Newman & Cannon, 1998
available from https://www.Philippine-Sea-Slugs.com/Look-alike/Platyhelminthes/Pseudoceros_scriptus/Select.htm