Black hitchhiker crabs

[h4wk]

Hello good people,

I've been hearing a loud clicking sound ever since I got the live rocks and I thought it was a pistol shrimp but I just got the opportunity to capture this little guy yesterday and today I saw two of them. Are they the ones making the loud clicking noise?

Are they bad news? I read they generally are, I have them in my aquarium for three months now with two cleaner shrimps, two clown fish and two urchins and they are all fine. A few snails are dead though. Coral wise I only have a torch coral that looks healthy.

 

[KJ]

Mithrax sp. and the clicking noise come from Pistol shrimp. Where does your live rock come from?

 

[skilos1]

I agree with the minthrax, look at the claws to be sure, they are usually flat at the top so that they can grab algae to eat.

 

[rkpetersen]

+1 on Mithrax aka Emerald Crabs. Beneficial algae eaters for the most part. Don't really attack corals that I've seen, although they will sometimes scrape and pick at stuff on the margins of the corals, causing the coral to close up.

 

[h4wk]

Thank you all for you replies. I was a bit worried whether they would kill smaller fish if I added them but I feel it's safe now.

Regarding the origin of the rocks I have no idea but maybe it's worth going by the pet shop I got them from and learn a bit more