Dear Nishina and Chikako,
I'm afraid this is another puzzle. This animal does not seem to be either N. nivalis or N. subnivalis. As I said before, Baba described N. subnivalis as having the mantle edge bi-colored, with an orange-yellow outer band and an inner yellow band. The rhinophore clubs are reddish purple at the tip and white below. The gills are usually all white but can sometimes have one gill which is yellow-tipped.

The mantle border in this animal appears to be an orange-yellow band broken into a series of elongate marks. The rhinophore club has a bright orange red tip and the gills are colourless. The mantle spots in all photos I have seen of N. nivalis are orange, they are irregular in shape and quite diffuse around the edge. In this animal the spots are a uniformly round and quite red in colour. I would suspect this spevies may be unnamed. It will certainly be necessary to look at its anatomy before we can say nay more about it.

Best wishes,
Bill Rudman