Is this a gorilla crab?

[Froggieboy]

this crab came of my live rock, and at first I was certain it was a gorilla crab because of the hairy legs. But when I did some more digging I am not certain anymore. It does not have the white eyes and the legs are the only things that are hairy. His body isnt.

 

[Donya]

Do you have a top-down pic of the crab showing the carapace shape?

From this pic it looks to me more like it may be a Mythraculus (Mythrax crab, Mythrax sculptus being the commonly sold species) or possibly a relative. Maythraculus can come in colors other than green and reddish brown is pretty common, even closer to black sometimes. Although it's not completely clear from the photo, the claws appear to be curved (I presume there would be an opening in the middle when closed) with spoon-shaped tips, which is characteristic of those crabs. Mythrax can have VERY hairy legs and a bit of hair on the carapace, so that in itself does not mean it's a bad crab. The only thing that stands out as unusual for a Mythraculus to me is how dark the claws are relative to the body (although you can get very dark crabs, it's usually more uniformly dark).

Gorilla crabs, which usually means Xanthid crabs, typically have short, very thick claws ending in a point rather than a spoon shape. This crab definitely has spoon-tip claws. What I can't tell is carapace shape and whether there's a gap in the middle when the claws are closed or if it's more flush, but at any rate I don't think it's a typical gorilla crab.

EDIT: I should say Xanthids that are typically hitchikers on live rock have the thick, short point claws but there are some exceptions as it's a big group with many species and there are other claw shapes out there in that group. I just mean that from this pic it still doesn't look like what usually gets called a gorilla crab in the hobby.

 

[Froggieboy]

Do you have a top-down pic of the crab showing the carapace shape?

From this pic it looks to me more like it may be a Mythraculus (Mythrax crab, Mythrax sculptus being the commonly sold species) or possibly a relative. Maythraculus can come in colors other than green and reddish brown is pretty common, even closer to black sometimes. Although it's not completely clear from the photo, the claws appear to be curved (I presume there would be an opening in the middle when closed) with spoon-shaped tips, which is characteristic of those crabs. Mythrax can have VERY hairy legs and a bit of hair on the carapace, so that in itself does not mean it's a bad crab. The only thing that stands out as unusual for a Mythraculus to me is how dark the claws are relative to the body (although you can get very dark crabs, it's usually more uniformly dark).

Gorilla crabs, which usually means Xanthid crabs, typically have short, very thick claws ending in a point rather than a spoon shape. This crab definitely has spoon-tip claws. What I can't tell is carapace shape and whether there's a gap in the middle when the claws are closed or if it's more flush, but at any rate I don't think it's a typical gorilla crab.

EDIT: I should say Xanthids that are typically hitchikers on live rock have the thick, short point claws but there are some exceptions as it's a big group with many species and there are other claw shapes out there in that group. I just mean that from this pic it still doesn't look like what usually gets called a gorilla crab in the hobby.

Thanks for replying!
If it is a mythrax crab, is it safe to put it in my reef tank? I am pretty new to crabs in the hobby so I dont know haha

 

[Colin_T]

Crabs should not be kept in fish tanks because they eat everything they can catch. There are a few filter feeding crabs and small coral crabs that are fine, but any crab that gets bigger than 1/2 inch will cause problems. If they don't eat everything, they push rocks over and rearrange the tank.

 

[Donya]

I am late with a response but this does still look like a weird variety of Mithraculus to me. The dark claws are still odd to me but I've since seen some images of less common Mithraculus species that have darker coloring there, so I guess that's just part of the range of variation for some. There are a bunch of species in the same genus that are functionally the same in terms of size and behavior - not that big (legspan of a couple inches usually), omnivores with preference for eating encrusting things like spirorbid worms, algaes, and so on (which will pretty much always be the case for spoon-claw crabs, including hermit crab species with the same claws). Some very small snails like small Nerites can be at risk but this can be said with other commonly kept clean-up-crew hermits that have similar claw shapes.

I have seen similarly red/white mottled Mithraculus IDed here and there on the web as "banded clinging crabs" but am not entirely convinced the common name is getting applied to just one species in those cases.

Crabs should not be kept in fish tanks because they eat everything they can catch.

Mithraculus crabs are very commonly kept with fish with no issues, provided it's not something extremely tiny like a neon goby being put in close quarters with it. Unless there are some exceptionally large Mithraculus out there that I'm not aware of, hey are not big/strong enough to destabilize rocks that are well stacked enough to be resistant to other common cuc animals. I've kept quite a few Mithraculus myself with fish with no issues, both M. sculptus and other strange ones that I never concretely IDed. The various Mithraculus I had in the past all behaved similarly to some of the Calcinus hermits I've kept.

 

[Froggieboy]

Hi! Thanks for your response, sorry mine is late too hahahaha. I put him into my twelve gallons which is free pf those pesky parasites that came with my live rock in my new 50 gallon. It is in with a clown and a coral goby and some corals. Just munching on the algea and I see no damage on the corals or fish whatsoever. Really beautiful and peaceful guy! It even molted already. Awesome guy