Finding one of these sapsuckers is indeed a treat.  They are nocturnal, so discovery generally involves looking very closely at the algae in the shallows and determining whether it’s an animal or a plant.  The jensenae is often confused with the Polybranchia samanthae or Cyerce elegans.   Though they can autotomize their cerata (as seen in a few images below), they do not do so nearly as readily as the samanthae.  When I spotted a Mourgona (?) sp.#5, I also questioned whether it was a juvenile of this species.  The individuals documented here were between 25 & 40 mm (1″ – 1.5″).  They were found in less than 2 metres of water, on rubble and algae covered rocks in semi-protected areas of Makena and North Kihei, Maui.   To 2 inches (50 mm).  See Sea Slugs of Hawaii for more taxonomic info and photos.