What's this crab?

[elefink]

So once again, I'm wondering what this hitchhiker that came on my live rock?

There are three of these guys in my tank now. Two have bodies about 1/2" and then the legs. The third has a body of nearly an inch. They appear to eat microalgae, but my gorgonians were eaten up over two days, and I don't know who did it.

https://scontent-iad3-1.xx.fbcdn.ne...=afca3ebf5a68fb7f9f69ce8ad26cb7fe&oe=5D077D63

 

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https://scontent-iad3-1.xx.fbcdn.ne...=1dc5fbcbc5dd9769d31aabccf4e82be2&oe=5D3E6F2D

 

[elefink]

 

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[elefink]

As you can see, the claws are small and have a flat aspect rather than sharp or pointy.

 

[scattered]

Looks like a red mithrax.