Click the thumbnail photos to enhance!
To add some confusion: there is a picture very similar to the above specimens on http://www.discoverlife.org, also with 4 marginal bands, but there are pictures of 2 specimens from the Philippines, from Kalipayan, Pangalao Island and from Anilao, Luzon Island, which lack the outer yellow rim that is they have only 2-3 marginal bands, but reverse colours, a broad orange margin, a black submarginal band and innermost a thin yellowish/white band. The specific name 'bimarginatus' means two margins, but this species has 3 - 4 marginal bands...
Let me quote Marcela Bolanos at LifeDesks:
"External morphology: white or cream dorsal surface with three marginal bands in the following order from the inner to outer: yellow-green, black and an orange rim. In some worms there is also a fine median white line that ends before the posterior margin. On the ventral side is pink-orange with the three marginal bands. The pseudotentacles are formed by simple folds of the anterior margin. Presence of a cerebral cluster formed by about 30 to 40 eyespots and the marginal eyes can’t be detected because the presence of the intense black band. Ruffled pharynx with folded lateral branches."
How to cite:
Köhler, E. (2018), published 7 April 2018, Pseudoceros bimarginatus Meixner, 1907
available from https://www.Philippine-Sea-Slugs.com/Look-alike/Platyhelminthes/Pseudoceros_bimarginatus/Select.htm