Pest crab?

So I think I have this pest crab maybe more. Here is 2 pictures of his shell. I found a shell like this on one side of his aquarium and this one I found on the other. Is it common for crabs like this to wander around the aquarium or do they stay in one area. It hasn't been that long since I saw the last shed, less then a month. So what I am wondering is should I really make an effort to get it/them out and how or is it harmless and let it go?

 

almost looks like an acro crab, do you have acros? and his molt could have been blown along by your PH's.

 

That is true I didn't think about it blowing around by power head and yes I do have acros but they are small frags except for two colonies I just got not long ago which was long after I found the first one.

 

Looks like a pest to me.

 

OK heres the deal...I took a flashlight to my new green/yellow acro colony I got because it seemed most likely to have a crab in it. Low and behold theres a crab in it. The other shell I saw like a month ago seemed bigger then the one I just saw and posted(this one was the size of a dime other was almost a nickel). Now another question is how resilient are crabs? None of my rock came right out of a tank and into mine without either being boiledor sitting dry/almost dry, or out of tank for a while. The only rock I would think it came out of was one rock that was sitting in like an inch of water for like a month or two.

 

if its an acro crab, its most came in with the acro. my understanding is they help eat any algae thatmay be on the acro. wso not necessarily bad, but theyve also been known to sometimes disturb zoas and such.

 

i don't know much about these crabs. but my motto has been "if there is a doubt, get it the hell out." if acro crabs are not bad, then forget my saying. otherwise, i say flush em.

 

personally i dont like the flush way , not really fair to any of the critters. . into the sump, or back to the lfs.

 

well the acro looks healthy so iassume its a good crab but im going to keep an eye on it
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So I found another crab shell in my aquarium. I think this is a different crab, as I mentioned before I believe there are two different ones. I have attached 2 pictures.