strange crab

[dolfans]

I have a strange crab in my tank. It is flat with strips . Anyone know what type of crab this is? Is it harmful?

 

[nas19320]

Could be a sally lightfoot. Does it have bright green markings?

 

[slick]

I agree, without a pic though it will be hard to ID.

 

[dolfans]

It has light green stipes on it.No, It does not look like a spider it looks like a emeral crab but flat.