Finding this teensy teensy sapsucker was indeed unexpected.  I brushed against a batch of caulerpa sea weed in a shallow, rock filled intertidal zone and noticed that one of the segments was actually moving.  These little “exquisite” sacoglossa are no bigger than 7 mm and this one was a little less than that (i.e., no bigger than 3/8 of an inch!).  Apparently, the greenish colour is more typical of individuals found in shallower water and brownish individuals live in deeper waters.   See Sea Slugs of Hawaii for more photos, natural history and taxonomic history.