Unwanted crabs...?

[Jenn_737700]

So I have this 10g nano reef, and its all cycled and everything, but I have some crabs. A teddybear crab which is only about half an inch, im not too worried. But this other brown one is an inch and a half ( a hitchhiker crab? ) I caught it with a net. But im not sure what to do with it? I know it sounds dumb, but, like do I flush it? what do I do? also, how do I get rid of a bristleworm?

Thanks for your help