Brownish, white and blue-grey marginal lines.
The Mantle Margin: This is the absolute dead giveaway for this species. G. hikuerensis features a highly ruffled mantle edge with a very specific, multi-banded pattern. Looking closely at your macro shot, you can clearly see the outermost white border, followed immediately by a stark, greyish-black submarginal line, and then a paler brownish-white band before the speckled body begins.
Speckled Dorsum: The central part of the back (the dorsum) consists of a tan or light brown base that is densely packed with tiny, opaque white speckles, giving it an almost textured, sandy appearance.
Rhinophore Detailing: If you look at the sensory tentacles (rhinophores) near the front of the slug, they are translucent but feature a very distinct, solid white vertical line running straight up the anterior and posterior midlines.
Branchial Plume: The gills at the rear are relatively simple and translucent, faintly edged in a darker brownish-grey.
Ecology & Behavior Diet: Like other members of the Glossodoris genus, they are highly specialized sponge feeders. They use a radula (a tongue-like structure covered in microscopic teeth) to scrape away at specific toxic sponges on the reef.
Chemical Defense: Because they lack a protective shell, they sequester the toxic metabolites from their sponge diet and store them in specialized glands right around that heavily ruffled mantle edge. The contrasting black and white bands are a classic example of aposematism—a visual warning to predators that they are highly unpalatable.
