Click the thumbnail photos to enhance!
At the Sea-Slug Forum are pictures of very similar looking specimens from Heron Island (Great Barrier Reef) and from Reunion Island, pictures of more variants including similar specimens from the Marshall Islands are at Kwajalein Underwater,
these variants are in IPN as Sclerodoris sp. 2 at page 188:
Gosliner, Terrence M., David W. Behrens & Ángel Valdés. 2008. Indo-Pacific Nudibranchs and Sea Slugs. Sea Challengers Natural History Books.
Gig Harbor, Washington. 426pp.
Let me quote the description: "This species is similar to Sclerodoris apiculata but with more regular depressions that resemble sponge oscula. there are dark spots in the center of each depression."
More information on Sclerodoris apiculata are on Bill Rudman's Sea-Slug Forum!