It does resemble a mantis but looks more like a spearer mantis which can do okay with a reef tank but not good for your fish. I have a mantis that has the "boxer appendages" and he looks a little similar to your guy but still different. So far he is coexisting great with my corals but not the fish or snails. He's a mean little bugger. Check out utube and search for the mantis video. That will give you an idea of what you are dealing with.
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