ID another critter?

[Bertico78]

Just found this new "stowaway" in the tank. Anyone know what type of crab that is and if it's beneficial or detrimental to a FOWLR tank?
Thanks!

 

[billie6227]

Looks like a porcelain crab, and those are reef safe.

 

[Aquarist007]

check here---I think it is an xanthid crab

http://www.melevsreef.com/id/crabs.html

 

[paraletho]

I think Capn is on the right track looks more Xanthid to me (Mud crabs or rubble crabs). They sit more upright on their legs with the carapace tilted down in back. Exact species ?

 

[greenbean36191]

Neither of the above. Porcelain crabs aren't "true" crabs and they have 6 walking legs rather than the regular 8 of true crabs. Xanthids usually have black tipped claws, but the dead giveaway here is the stance with the legs splayed out as well as the body that's narrower at the back than the front. It's a grapsid, or clinging crab, of some sort. You're almost certainly not going to be able to get it identified to species. Even for adult crabs that's almost impossible in most cases without consulting a specialist. For juveniles, even then it might be impossible.

Some of these guys are fine, and may be commensal on benthic critters. Others are pretty destructive, especially as they get bigger. Personally I never trust any crabs since they're almost all opportunistic.