This little bubble shell is absolutely gorgeous, especially when caught in the light of day. They are generally nocturnal, but this one was out in the open in the heat of mid-day wandering across the sand and rubble of a tidepool formed by an accretion platform in Ma’alaea Bay, Maui.  Bill Rudman’s site, the Sea Slug Forum has some fascinating photos of the animals’ anatomy and some of the variations in colour of both the shell and mantle.  Sea Slugs of Hawaii, provides more information re colour forms, size and taxonomy related to the islands.  The Hydatina physis has a number of common names:  Brown-lined Paper Bubble Shell, Green-lined Paper Bubble Shell, just plain Paper Bubble Shell and Rose Petal Paper Bubble Shell.  The latter is my favourite and certainly suits this rose coloured, blue-lined beauty.  Approximately 50 mm or 2″.