That is a sea hare. Named aptly due to the face and long "ears" of a wild hare. Strictly algae grazers. Short lived in home tanks. I can't tell if it's your camera or hare but I see green. If it;s green and smooth it;s a dwarf. If it is spiky and brown it's a full sized model. They get large. About 5" long and very stocky. Will keep your glass CLEAN. They will also eat longer hair algae and some briopsis. One of my favorites of the strange. Rumor is they have enough toxin in them to wipe out a tank. I have a very well suited Euroreef skimmer, when mine died it did nothing to the quality of the tank.
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