The Ringed Sapsucking Slug is one of the first sapsucking slugs I came across on Maui — and by the dozens.  They will often congregate and mate in huge masses, covering themselves in sand or wriggling around and on top of each other.  Their beautiful blue and gold rings and violet-tipped rhinophores generally go unnoticed, but on close inspection these rather flat, boring looking animals are quite beautiful.  I have found them in less than 1 ft of water and down to 20 ft — always in fairly protected back reef areas and lagoons.  For more info, as always, head to Sea Slugs of Hawaii.  To approx 2.1/2 inches or 65 mm.