This is a Risbecia tryoni nudibranch. It is also known by the name Hypselodoris tryoni. It is similar in appearance to Goniobranchus geminus, Goniobranchus kuniei and especially Goniobranchus leopardus, although it lacks the wide purple mantle edge line present in those species.
Size: 8cm
Depth: 18m
Divesite: Bianca and Serena, Lembeh
Country: Indonesia