Black Emerald Crab?

[sipos624]

I was looking at my sump and i found this guy. Has anyone heard of a black emerald crab. Just wondering i think he's unique. Sorry the pictures are so bad; its hard to do macro shots without an SLR. Thanks,
-Mike

[chrisqueenz]

Looks like an emerald....

[tprize]

I think I have heard of these things being called stone crabs and if I recall right they are very very bad at killing fish.

[IslandCrow]

I don't know, that looks exactly like a Mithrax crab to me. I've seen some very dark green (almost black) and red, but even though I've never seen a black one, that certainly doesn't mean they don't exist. My bet is on that being a black "emerald" crab.

[02REDZ28]

I've had several of them in my SPS tank. They are a melanistic form of the green Mythrax crabs commonly called emerald crabs. They are opportunistic just like any other crab and this is magnified in a low nutrient tank. The crabs were snipping off the tips of my Stylophora and Acropora corals as well as walking away with frags that weren't secured to the liverock.

I removed them from my tank and placed them with some liverock in my sump. They exist there just fine while cleaning up any food stuffs that make it down there. If I were you, I'd keep them out of the display.

[mousefish]

I had a crab similar to yours in my reef once. He was also an omnivore. He ate the algae but also would occasionally take a swipe at the smaller fish that would swim by. Needless to say, it was not an occupant of my tank for very long...

[jjmcat]

I dont trust any mythrax crab.They are a hit or miss on being helpful or harmful to your reef.

[msuzuki126]

To the sump!

[Frick-n-Frags]

does it have the white "spoons" on its claw tips?
does it have the red inner elbow joints?

If not, to the sump.
If so, it is a black color variation of the good mithrax. the rest of it looks mithrax family, that's for sure, but which mithrax species?


IMO, the red elbow ones are 100% reefsafe because I have had many over whatever 15 years. of the however many 20? 25? I've had, not one single one did anything but its job. they will make you nervous, climbing on everything with reckless abandon, but at the end of the day, the coral is cleaned and a few frags are knocked over from them cleaning.

[andrewkw]

i've had 2 of these guys and they are evil if you ask me. I'm not positive but i believe they killed my small red starfish and perhaps even a baby maxmia clam. Better safe then sorry so I removed the first one to the sump and killed the 2nd one.





here's the first one, which was actually smaller then the first. I don't think they are the same one since it would be very hard for him to make his way back into the display but you never know...



I had to take out 99% of the rock in my tank to get the first one out. The 2nd one as soon as i saw it in the corner i removed about 30% of the rock and got him out. Even found a peppermint shrimp i haven't seen in months and months.

[mousefish]

My main problem with the black crab was that it started small, but seemed to rapidly grow to twice the size of the typical mithrax crabs. Definitely worth getting them out of the tank if possible.

[Neezy]

I have one, this is like third one ive ever seen. im positive these are emerald mutations

[Snowboarda42]

He looks evil, I want him for my sump! I'll name him "dungeon master"

[reef2]

ive seen 2 of these at my lfs. they where at least the size of a half dollar and black.