Crazy looking crab showed up today!

Me and my wife tried getting it out. We put some dried brine on the aquadose and set in the corner, she came out slowly and jumped back in her rock whenever anything got close. She'll push away the hermits, but it's afraid of everything else. Doesn't seem aggressive at all.

I'll keep my eye on her, but I think we are going to leave her in the main tank. I'm sure it's been in there for awhile, and nothing has shown any distress.

She does not play dead, which doesn't seem to match the current IDs.

 

I keep a couple of little emeralds in my 300 to go after Valonia too. They don't look like that.

 

The right way (and only to my knowledge) to ID emerald crabs is to check the inside of the joints of there legs, if its red then you got yourself an emerald.

Not sure if i expressed myself right (im french after all) but if its not clear let me know and ill try to clear it up.

Marc.

 

I'll see if I can get it to come out again, and then I'll take a look. It doesn't move around the tank at all, or even come out, unless there is food.

 

Although it might belong to the family of the mithrax, I dont think it is an emerald. Emeralds have hairy legs with a green, shaved torso. Then again, there are some crabs that decorate their armor with algae for camouflage. ;D

I think unless you find one that best looks like your crab, dont make a definite ID on it. For all you know, it might be beneficial. You cannot stop these crabs from ever creeping in your reef because they always will. They hitchhike on rock to coral.... it is impossible.

 

I think I have the same crab!

I know I have at least two of these crabs in my tank. One is much smaller than the other. Here is a photo of the larger one. He seems to only be interested in eating algae. I still can't really find anything on the internet about what kind of crab it is.

 

Thats a hairy crab.....

 

I use to love emerald crabs, use to defend them when people talked smack about them. They are great algae eaters, but when the algae is gone, they go looking for other food sources and since ALL CRABS ARE OMNIVORES, they will eat just about anything. NO CRAB IS 100% REEF SAFE! The emralds I HAD ate my favorite slug the other day and they went bye bye! I caught the fudge packer red handed er.... "red clawed". I was moving something in the tank, and there one of them was, half shell in claw, eating it with the other claw!

So in my personal experience, emerald crabs=bad bad bad, die die die!!!!

 

The Emerald(Mithrax) is a member of the infraorder Brachyura. Inevitably all reef organisms have to eat to survive thus their really isn't any 100% guaranteed "reef safe" crab, shrimp etc. With that in mind you can break it down alittle further and say reef safe means the likelihood that an organism will eat other popular fish and inverts as well as corals.
Now as far as crabs are concerned, you would look at the many hermits that retain a small size, both in body, and more importantly in claw size (blue legs being an example). Then you have the Porcelain crabs that are filter feeders. They are quite safe with fish and inverts due to their diminished claws and filter feeding appendages.
At the other end of the spectrum, you have something like the Box crab, which will grow rather large and comes with big and powerful claws as this is a formidable opportunistc feeder! Other problem crabs are the decorator, Horseshoe and Pom-Pom and anemone crab.
In between these crabs listed above you have everything else, like your Sally Lightfoots, Emeralds, Arrow and the like.
Again, I still think that the picture is of a Mithrax crab. And really, unless you have small fish, again they are omnivores, they are a useful and worthwhile aquarium inhabitant in my opinion and others such as Anthony Calfo and Robert Fenner.
Hope this helps!

 

The crab has caused no problems. He still hiding mostly, but I did see him out in the sand the other day.

He hides from my small clowns, so I don't think he'll attack.

Thanks for the help everyone!