This is a very pretty flatworm and finding it wandering across rocks and sand in a tidepool was quite the treat.  Even as it moved it remained fairly circular in shape and its banded nuchal tentacles and purple-edged, varigated stood out against its white-speckled, goldish/brown body.   I hesitate to confirm whether this is a  Paraplanocera marginata — at least of the Hawaiian variety.  As Cory Pittman points out, “this animal looks less like the the Paraplanocera on John Hoover’s site and more like the Paraplanocera marginata on this site from Reunion Island. I have to agree with Cory, as well as his suggestion that “these Paraplanocera  may be separate species, both with broad ranges.”   Perhaps this will be cleared up sometime in the future.  Appoximately 1.5 ” or 37 mm, Ma’alaea Bay, Maui.