Solomon Island Sea Slugs

This inch-long nudibranch is crawling around on one of the wrecked Japanese World War Two freighters at Bonegi beach.   You can see the profusion of life here - the funny veined things on the right, the orange thing (I don't even know what sort of thing it is!) at the bottom centre and the unnatural looking blue algae or whatever it is at the bottom left.   From its perspective, this sea slug is really crawling around in an underwater garden.

unknown nudibranch
This beauty might be a Phyllidia varicosa, or perhaps a Fryeria menindie.   Nudibranchs eat all sorts of toxic creatures, including corals, and store the toxins inside their own body, making them distasteful to predators.   The nudibranches then advertise their poisons using bright colors, because it's better to have a predator avoid you completely than to bite you and then spit you out.
top view of Phyllidia Varicosa
side view of Glossodoris Sibogae

On the middle of this Glossodoris sibogae you can see the "naked gills" which give nudibranchs their name.

top view of Glossodoris Sibogae