Hitchhiker Crab, Good or Bad? WTD?

[Gwynhidwy]

I have not added any crabs to my tank because it seems that at best they are hit and miss for not harassing other inhabitants. Today I spotted a crab that must have hitchhiked in on my live rock. He is about an inch across including legs, cream in color with reddish brown/tan colored splotches all over. He has one darker brown, fairly large, proportionally to his body at least, claw. Anyone know what he might be? I don't know much about crabs, so any help would be appreciated. I'd really like to ID him so I can learn more about him and whether or not he should stay.

 

[Randall_James]

without a photo, it is almost impossible to ID (several thousand types of crabs)

Black pointy claws = bad sign
Hairy = bad sign
caught with live fish in claws = bad sign

 

[Gwynhidwy]

I was afraid of that. No digital camera. He is not hairy at all and his claws don't appear to be black, just dark brown, like maybe a chocolate color which is darker than his splotches. There aren't any fish in there for him to catch right now, but I'm worried about my shrimp.

 

[Gwynhidwy]

He looks quite a bit like a porcelain anemone crab, except that the ones I've seen haven't had the darker claw. If that is what he is, he probably won't love my tank as I don't have any anemones.

 

[Randall_James]

I have a few "not so good" crabs running around but they have not created a reason to go on the warpath so there they stay.

They came in on a load of rock I got from Tampabay saltwater..

 

[bertoni]

If it's a porcelain crab (not a true crab), it's fine to have. True crabs pretty much are all risky, but some don't seem to be very destructive, at least for a while.

 

[Randall_James]

<a href=showthread.php?s=&postid=10604090#post10604090 target=_blank>Originally posted</a> by bertoni
If it's a porcelain crab (not a true crab), it's fine to have.

what are they? just mildly grumpy? :lol:

 

[Gwynhidwy]

Thanks very much for the replies! I'll leave him be and see what happens. As near as I can tell he is a porcelain crab, and a cute one at that.

I'm curious too, why is it not a true crab?

 

[bertoni]

Well, biologically speaking, true crabs are brachyurans, and I believe the porcelain crabs are anomurans. I can't remember which piece of anatomy divides the categories. Wikipedia is more useful than I am:

As decapods (meaning ten-legged), Anomurans have ten pereiopods, but the last pair of these is often hidden inside the gill chamber (under the carapace) and is used for keeping the gills clean. Since this arrangement is never found in true crabs, a "crab" with only eight pereiopods must be an Anomuran.

 

[Angel7989]

i found a crab today in a piece of live rock at the LFS where im buying my mantis shrimp.
one of my friends who works there snaches the rock and points out to me that this is a BAD CRAB! haha
so he throws it in the tank with my mantis and in ONE hit she knocked its claw clean off for a tasty snack and left the crab to hide somewhere. but i bet hes going to be a good breakfast! =P

 

[phil519]

<a href=showthread.php?s=&postid=10605261#post10605261 target=_blank>Originally posted</a> by Gwynhidwy
Thanks very much for the replies! I'll leave him be and see what happens. As near as I can tell he is a porcelain crab, and a cute one at that.

I'm curious too, why is it not a true crab?

A "true" crab will have four walking feet on each side of it's carapace.

With the porcelain "crab" (Porcellanidae) - it only has 3 on each side. Another sure give away is when it opens it's mouth to filter feed the water. The claws may appear large on these crabs but they are harmless.

More wiki info

Also much more detailed info by Dr. Ron Shimek on Crabs here