Mystery Crab ID (can't find anything like it online)

[Speedy77]

Hey guys!

Here's a small album of the crab in question:
http://imgur.com/a/Rsdjh

Not sure if any of you guys are super knowledgeable about crabs, but if I could get any info on this guy that would be awesome! I've had some disappearing zoanthids for a few months, so he may be the culprit. Here's the crab's story:

A few weeks ago I added a female emerald crab in my tank to take care of some lingering bubble algae in my tank. A few days after adding it I see this crab for the first time. I assumed based upon the way its back looked that it was the emerald crab that had just molted, and whose new shell hadn't colored up yet (this other crab has kind of a marbled pale purplish and white shell). I didn't think anything of it, and saw my emerald crab later that week looking normal.

Today I saw the huge crab again (about the size of a half-dollar) just chilling under a rock, and this time I knew it wasn't the emerald crab. I was able to capture it and confirm that it was a male and not the emerald crab, and now I'm showing it to you guys! I'm so proud I finally have my first hitchhiker and potential pest!

The strangest thing about the whole story is that I haven't added any rocks that he could have come in on in well over a year. My only thought is if he came in on one of those pieces while he was extremely small, and eventually grew to this size. It's just surprising to me that after all these months I haven't even seen the guy. I went from a 20g long tank to a 40B about a year ago, so maybe he came in with the live sand we bought? No idea. My thoughts are he may have just come out more recently due to the female crab's presence in the tank. Either way, cool stuff!

Let me know what you guys think. Thanks for reading!

 

[jraker]

that looks bad. i dont know what it is, so i wont tell you to keep it or get rid of it yet. as long as you havent released it into your main tank yet, you should be fine. personally, i think it is bad. any other input?

 

[sam.basye]

I'm thinking a stone crab.

 

[jraker]

yeah, it looks like a stone crab, or a crab from the genus xanthidae. from what i have seen, they are carnivores and will eat any snails and some corals like zoas. bad crabs. get rid of it.

 

[Speedy77]

Good to know, thanks for the advice!
Like a stupid person I neglected to put the lid on the floating incubator, so the guy made it back into the tank. I don't think he'll do any serious damage over the next few days, but I'll try to track him down again to get rid of him. Thanks for the heads up!

 

[jraker]

you can go to your tank in the middle of the night, and shine a flashlight at it. i do that sometimes, and my emerald crab will get stunned.

either that, or you can use the bottle trap method:

 

[Betta132]

He's a pretty cool crab. Do you have anywhere to keep him, like a sump or refugium? I think he might be a box crab or shamefaced crab, but it's hard to tell from the back. Did you get any photos of his claws?
That bottle trap design will work well, you just have to lay it on its side so the crab can get in. Bait it with clams and you should catch him pretty quickly.