Dwarf Sea Hare (Aplysia sp.) アメフラシ
This is a very small Sea Hare. It looked like Aplysia parvula which used to be considered a worldwide species. It has been recently split into several species. Aplysia japonica is found in Japan and Korea, but it is found in mainland Japan and Jeju Korea. アメフラシ is found in the Indian Ocean and the Philippines. It seems to resemble Aplysia nigrocincta more and the fish around here are more like the fish in the Philippines too. The Japanese name I have used is general name for Sea Hares. Amami 2025
Another picture of the mystery Sea Hare. Amami 2025