Cratena affinis from Hachijo Is., Japan

Dear Rie,
I am sure you are right. Although the colours are rather different from the painting in Baba (1949) this fits in all major respects Baba's Hervia affinis. In particular the two large flattened rings on the rhinophores are very distinctive, and so are the inflated cerata which abruptedly end in a thin tapering papilla at the tip. Baba notes the body is covered in white spots, as is your animal, and describes the cerata as having fine, longitudinal, opaque white lines and a dark digestive gland. In your animal only traces of those lines are present and I presume the colour of the digestive gland duct is dependent on the slugs recent diet. I can't check in this photo for the presence or absence of the two orange red patches on the head, that Baba describes. On balance I would agree that this is Cratena affinis. The most appropriate genus for this species must wait until more material is examined.
Best wishes,
Bill Rudman.