rock-boring crab?

[JKurtz]

Can anyone help me identify a crab that stowed away into my tank in some Fiji rock? I noticed it several months back when a pile of rock dust was suddenly pushed out of a hole in one particularly craggy piece of rock. Using a flashlight, I could see that there was a crab inside the hole, but it was too secretive to identify. Sometimes it would block up the entryway into its hole with puka shells from the substrate (presumably to protect itself when molting).
Now, the crab is significantly larger and seems to have moved operations to a network of tunnels in the substrate underneath the rocks, rather than within the rock itself. I've caught a few quick glimpses of it as it rushes out from hiding to grab a piece of nori left behind by my yellow tang. It's pretty drab in coloration--dark gray to almost black with very faint light spots on the top and tan on the underside. Eyes are red. Claws are fairly impressive, but it hasn't done any damage to any inverts as of yet.
Sorry the description is so vague, but I don't have much to work with.
Anyone have any similar experience?

Jeff

 

[DrGrotto]

I purchased some live rock to start my new tank back in June and had a really small black crab sitting in the bottom of the box when it got to my home. I put the crab in the tank as it was cycling, not expecting it to live, but hoping it would. I too have noticed something that has been building a shell and substrate nest in my rock. I had no idea what it was and just let it go. The other day I was watching my tank and noticed this a black crab with red eyes at the entrance of a cave in my rock. I beleive that it is the same crab that came in my Live rock shipment, and I think it's the same kind that you have.

I don't know what he is called yet. Like you said his claws are impressive to say the least. If I ever find the name, I'll let you know...

 

[beerbaron]

i also had one of these guys. they shouldnt be considered reef safe. to catch them wait till about an hour after lights are out. sneak up to tank and turn flash light on. you should be able to find him. then just grab em with your hand.
if you dont want him out, it is still a good time to check em out.

 

[wade1]

There is also a chance its not a crab at all but a mantis. Its a common mantis shrimp behavior to plug up its cave entrance and hide it from view. Either way, it would likely be worthwhile for you to remove the rock and flush the hole with freshwater until the beastie comes running out.

Good luck.

Wade

 

[DrGrotto]

Don't they eat hermit crabs? I have hermits and they all seem to be intact. I hope it's not a mantis...