Is this crab bad or good?

[ILikeFish!]

Btw in the video the crab looks a little green but it’s not it’s like red and tan.

 

[ReefStable]

I know I'll get some kickback on this... However...

I'm going to say if you didn't add it, call it bad. Usually the hairy ones are always bad. This one I have no idea what it is based on those legs. So I would call it bad for the tank by default.

Maybe others have more input on what it is though.

 

[Pstreet]

Might be a Sally Lightfoot crab. Research those. I had one for awhile and it was tan with the striped legs. Mine never bothered my coral and only became a problem when it got bigger: killed my hermit crabs, snails and pistol shrimp, then started trying to grab the fish.

 

[Reefing102]

Perhaps Mithraculus forceps? Mine has been safe though very reclusive.

 

[Fish Styx]

It's a ruby mithrax crab.

 

[leo12345]

It's a ruby mithrax crab.

No it’s not, I used to have one and they look completely different.

 

[ILikeFish!]

I know I'll get some kickback on this... However...

I'm going to say if you didn't add it, call it bad. Usually the hairy ones are always bad. This one I have no idea what it is based on those legs. So I would call it bad for the tank by default.

Maybe others have more input on what it is though.

I’m definitely going to remove it I’m just curious if it’s bad or not anyway.

 

[Fish Styx]

No it’s not, I used to have one and they look completely different.

Edit: I just rewatched the video, and I think you may be right. 1) it's legs aren't hairy enough, and 2) when it is out of the hole with it's claw in front, you can see (faintly) possible fans in front of it filtering (around the 40 second mark). It could be a Porcelain Crab. Either way, @ISpeakForTheSeas is right: better pics/ videos are needed.

 

[ISpeakForTheSeas]

You may need to remove the crab and get some clearer pics of it - pics of the top of the shell showing the full body of the crab, and pics of the claws (preferably from the front of the crab) would be helpful.

 

[ILikeFish!]

You may need to remove the crab and get some clearer pics of it - pics of the top of the shell showing the full body of the crab, and pics of the claws (preferably from the front of the crab) would be helpful.

I got another video but it’s hard to get a video of it.

 

[PeterEde]

I've not removed any crab from my tank. My live rock came with quite a few crabs. So far haven't found a need to remove any. Including red crabs with black claws. They all seem to stay hidden in the rockwork

 

[ISpeakForTheSeas]

I got another video but it’s hard to get a video of it.

Yeah, a top-down, straight-on pic of the top of the crab would help - you need the aerial perspective to really see the shape of the shell/carapace.

 

[ILikeFish!]

Yeah, a top-down, straight-on pic of the top of the crab would help - you need the aerial perspective to really see the shape of the shell/carapace.

That’s going to be hard to get because it rarely comes out. What do you think it could be just from what you can see from these videos?

 

[Katrina71]

Baby Florida stone crab?

 

[ISpeakForTheSeas]

That’s going to be hard to get because it rarely comes out. What do you think it could be just from what you can see from these videos?

My best guess (which may be wildly inaccurate) is a Chlorodiella species like the one linked below:

https://www.floridamuseum.ufl.edu/wp-content/uploads/sites/23/2023/03/new_4.jpg

 

[ILikeFish!]

My best guess (which may be wildly inaccurate) is a Chlorodiella species like the one linked below:

https://www.floridamuseum.ufl.edu/wp-content/uploads/sites/23/2023/03/new_4.jpg

I’m pretty sure that’s exactly what it is. are they bad?

 

[ISpeakForTheSeas]

I’m pretty sure that’s exactly what it is. are they bad?

They're safer than most crabs, but I'd say probably reef-safe with caution (not many people keep them, though, so that's from a small sample size to work with).

They're technically Xanthid crabs (which are generally not reef-safe), but these are generally very small, and at least one related species (Chlorodiella nigra) is sold occasionally as a "Black Mithrax Crab." I know at least one was kept without causing problems until it was full grown (then it reportedly started eating small inverts), but even emerald crabs are known to sometimes cause issues when larger.

I'm fairly confident you've got a young Chlorodielline crab of some variety there, probably a Chlorodiella sp., possibly C. nigra, but I'm not entirely sure.

The pattern on the legs may change a bit as it ages, and it should develop a somewhat rougher carapace, but it should stay small (adults of most of these species have a carapace size typically right around ~0.4"-0.75" full grown, so it really shouldn't pose a threat to most livestock - no guarantees with corals though) - there are claims that these can reach 8 cm/~3.14" full grown; I have seen absolutely no evidence to support that (even if you include the legs in the measurements).

I have seen one exceptionally large individual with a carapace width slightly less than 3 cm (it was ~1" carapace, and ~6 cm total counting fully outstretched legs); even at that size, it should be around the same size to somewhat smaller than a grown emerald crab.

I have also seen these for sale as "Black Mithrax Crabs" (no, they are not Mithrax crabs, nor are they closely related) - they're purportedly reef-safe, but I've also heard they may eat small inverts (like brittle stars).