This Sclerodoris is fairly rare, or simply not seen because of its incredible ability to mimic a sponge.  In fact, when I first encountered one, I wasn’t entirely sure I was photographing a nudibranch. Its branchia could just as easily have been a feather duster worm poking through the cavity of a sponge.  It was in resting position when I found it and it never budged, never revealed its rhinophores and only occasionally withdrew its branchia enough to suggest it was alive.  In the fall of 2022 I came across 2 individuals in the same area of North Kihei — one was clinging to a rock in a surge zone and I thought it odd that a sponge could be thrown about and still hang on.  When I looked more closely I could see rhinophores and gills and distinct papillae.  When the surge settled down I was able to take some close up photos. The active individual was at least 60 mm.  So . . . look closely at those sponges, especially the ones with the deep pits . . and for other photos of the animal and more information, please see Sea Slugs of Hawaii.