Bulla piasiana is one of two species of Bullidae found in Hawaii. They are primarily nocturnal so it was a surprise to notice it feeding mid-day. However, it is doubtful I would have noticed its shell poking through the algae had my attention not been drawn to a diurnal Elysia ornatus feeding in the same area. These bubble shells are fairly common and can reach up to 39 mm. This particular individual was approximately 20 mm and was found in North Kihei Maui in less than 3 metres of water. For further information on this species please check out Sea Slugs of Hawaii.