What is this and i keep finding him on my toad stool.

[easyautocare18]

My toad tool looks like it being eaten. I have dipped it with coral rx. I was looking at it today I found this little guy on it and he was on it a couple of days ago. There are tiny little bugs on the toad stool to. maybe he is just cleaning the bugs off are maybe he's eating my toad stool. What is he do yall know?

 

[blaxsun]

It's a baby crab, but what kind I could not say.

 

[easyautocare18]

I definitely know it's a baby crab. But is it harmful to my toad stool? Or is it eating the bugs that are on the coral?