This is a very tiny, very beautiful headshield sea slug that appears to be quite rare.  Though our group of snorkelers and reef cleaners cover this area of North Kihei and Ma’alaea Bay fairly often, we have only come across this animal a few times. In all cases it was found in less than 10 ft of water in an algae and sponge covered rubble and sand area. One of the animals was found half-buried in a blue-grey sponge, perhaps its prey? They have both a siphon and a flagellum.  A flagellum can often enable mobility and with their large parapodia (wings), they have been known to swim.  For more information from the people who first recorded this animal on Maui, please see Sea Slugs of Hawaii.    To 8 mm.  TINY!