Another Mysterious Crab show up!

[Yuki Rihwa]

I need an ID for this crab, I'm random watch my tank in the dark with abit of blue light from my heater and I spotted some thing moving fast between rock and went to a hole in a small rock, I took the rock out and dip in freshwater and its ran out. All my rocks are dry rock I had for many years already and I did not add new rocks or any coral frags LOL

Long big claws and hairy legs with pattern color like zebra, body in deep black. What's it ID?
Few days ago I spotted a Cerith snail and a carcass of a tiny crab, and tonight is a bigger crab 1 inch in size. How the heck these thing keep showing up in my tank from nowhere?

 

[Yuki Rihwa]

I found my own answer
It's a Black Mithrax Crabs and I still don't know how and how long it's been in my system.

 

[ThunderGoose]

Handsome devil. Good candidate for a refugium/ sump.

 

[azreeftank]

I have one that is about 2” across It looked like an emerald when I first bought it (light green) and it grew into this looks just like yours. I was worried for years about it but could never catch him. He only comes to the edge of the rocks to eat when I feed the tank. Has never eaten anything and is a model citizen so i just leave him to clean up. So far mine has been reef safe and he’s going on 5 years in my tank. I have tons of LPS, some clams and smaller gobys and he is fine. Even see my mandarin hang out next to him and he’s larger than the goby. I say leave him in to clean up under the rocks and caves.

 

[Yuki Rihwa]

@azreeftank Thanks for the information and pictures, I still worry to put it back in my tank even it doesn't touch my clams last few months but its still a crab hehehe and Crab will eat anything they like or able catch at night time. Last night after the crab incident I check my tank again at midnight and guess what? I found many stomatella baby snails, I like them and I think the crab would eat baby stomatella snails or wipe them out since these baby very easy tasty target.

 

[Daniel@R2R Verified Admin]

Cool little guy! I agree that crabs are opportunists. If you've already caught and moved him to the sump. I'd say leave him there.

 

[azreeftank]

@azreeftank Thanks for the information and pictures, I still worry to put it back in my tank even it doesn't touch my clams last few months but its still a crab hehehe and Crab will eat anything they like or able catch at night time. Last night after the crab incident I check my tank again at midnight and guess what? I found many stomatella baby snails, I like them and I think the crab would eat baby stomatella snails or wipe them out since these baby very easy tasty target.

Yeah I agree if you already caught him put in the sump to be safe. Mine is too fast and smart and does not come out and since I have too much stuff to move I will leave in for now.

 

[Vincent100]

If he's out of your tank keep him out
I'v been trying to catch mine for months with no luck
Every time I feed my lps he's out causing trouble
They are strong ...he's pull a couple of corals from the front of my tank right under my rock work
It's not nice wakeing in the morning and have to check if any corals have gone walk about
PS .....mines a Beast , that's hes small claw in the pic ;Bored

 

[BillyBuckshot]

I have a tank with 3 small blue crabs. In the last 2 weeks I’ve had 4 mystery blue crabs show up. I can’t explain it. All were freshly dead, but the one today had climbed up to a platform in the tank and died. I think I’m losing my mind. There’s no reasonable explanation for it.