Umi-Ushi

It means "sea cow" in Japanese and it's English name is "sea slug" or "Nudibranch". We can see "horns" on their head so that's why they are called "Umi-Ushi". Their body color is colorful and very cute. I can watch them as long as I can stay in the water. The picture is the one I saw in Okinawa. He was enjoying his life in the beautiful sea. There is interesting description about this creature in Wikipedia.