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.net/v/t1.15752-9/55453695_2625030187525206_3298481157582094336_n.jpg?_nc_cat=101&_nc_ht=scontent-iad3-1.xx&oh=afca3ebf5a68fb7f9f69ce8ad26cb7fe&oe=5D077D63

[elefink]

https://scontent-iad3-1.xx.fbcdn.net/v/t1.15752-9/55910124_640035723104893_4905062937925779456_n.jpg?_nc_cat=102&_nc_ht=scontent-iad3-1.xx&oh=1dc5fbcbc5dd9769d31aabccf4e82be2&oe=5D3E6F2D

[elefink]

https://scontent-iad3-1.xx.fbcdn.net/v/t1.15752-9/55910124_640035723104893_4905062937925779456_n.jpg?_nc_cat=102&_nc_ht=scontent-iad3-1.xx&oh=1dc5fbcbc5dd9769d31aabccf4e82be2&oe=5D3E6F2D

[elefink]

https://scontent-iad3-1.xx.fbcdn.net/v/t1.15752-9/55453695_2625030187525206_3298481157582094336_n.jpg?_nc_cat=101&_nc_ht=scontent-iad3-1.xx&oh=afca3ebf5a68fb7f9f69ce8ad26cb7fe&oe=5D077D63

[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.