Crab

[Nella]

Think he's an unwelcome hitchiker that came with some live rock?

 

[NJH]

Sump it, do not kill it. But do not put back in your display.

 

[tekkengal]

It looks like a gorrila crab. They tend to hunt fish as they get bigger. @NJH advice is good, no need to kill it. Some people do smash them open for their fish to eat (if you want to kill it, rather let it not die for nothing).

 

[Nella]

Thanks
it's already in the sump . Will feed in there