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Let me quote the description of Pseudoceros dimidiatus by Marcela Bolanos at LifeDesks:
"Large body with deep marginal ruffles, and pseudotentacles formed by simple folds of the anterior margin. The dorsal side is velvety black with two wide median yellow stripes that begin at the pseudotentacles and end just before the posterior margin forming a narrow black median line. A wide orange marginal band surrounding the entire animal is present.."
The specimens #5, #8, and #9 fit the above description perfect.
Accoring to Gosliner et al. (1997) Is Pseudoceros dimidiatus "Highly variable in color pattern. Body black with an orange margin and wide yellow lateral stripes or zebra-like bars."
There were many pictures of colour variants from the whole Indo-Pacific (Mozambique, Tanzania, Kenya, Egypt, Saudi Arabia, Malaysia, Indonesia, Papua New Guinea, and the Philippines) at Nudi Pixel, this website is down, the pictures are gone.
There were pretty similar variants to the pictures #2, #3, and #4, from Wakatobi, Indonesia, and from Kapalai, Malaysia, both identifications confirmed
by Marian Litvaitis, and from Brunei Darussalam, identification not confirmed.
And there were pictures similar to picture #1 from Puerto Galera, Philippines, from Anilao, Philippines, both identifications not confirmed.
At Philibert Bidgrain's South-west Indian Ocean Flatworm site are some pictures of Pseudoceros cf. dimidiatus, which differs by two median longitudinal yellow stripes separated by a thin black line.
cf. is an abbreviation from a Latin word (confer) and means 'refer to' or 'compare with', here it means it could possibly be Pseudoceros dimidiatus or perhaps something closely related, or at least similar in appearance.
Gosliner, T.M., Behrens, D.W. & Williams, G.C. (1997) Coral Reef Animals of the Indo-Pacific. 314pp.
Monterey, California: Sea Challengers.
How to cite:
Köhler, E. (2019), published 4 January 2019, Pseudoceros dimidiatus von Graff, 1893
available from http://www.Philippine-Sea-Slugs.com/Look-alike/Platyhelminthes/Pseudoceros_dimidiatus/Select.htm