This may be a form of Costasiella kuroshimae, which as noted by the Sea Slugs of Hawaii site is a variable species. The coloration seems different enough from our other C. kuroshimae that we are keeping it separate for now. This animal was on a piece of Codium algae when first seen by Christina Sylvester. It measured about 4mm.
Created 20 March 2017
Updated 24 March 2017