"Probably Phyllidiella pustulosa. The pink pustules arranged in rough rings on the middorsum are reminiscent of Phyllidiella annulata, but in that species the pustules are not supposed to be compound, as they appear to be in the photo from Kosrae. I've seen specimens of what I call Phyllidiella pustulosa similar to this, although I have to say the identification is not 100% certain."