Anna’s Chromodoris (Chromodoris annae) アンナウミウシ also Anna’s magnificent sea slug size 5cm
An Anna’s Chromodoris is said to only feed on Petrosaspongia sp. sponges. It has also been seen aperently feeding on tunicates. There are some similar species. Look for the small black dots on the blue back and the short black line between the rhinophores. Amami 2024
A closer look at the same Anna’s Chromodoris. Amami 2024