Crab ID please. Thanks

[HumbleAsianReefer]

Just saw this crab today. Still trying to remove it n dump it in my refugium. Can anyone help me ID it? Friend or foe? Thanks in advance

 

[ISpeakForTheSeas]

Probably a Chlorodiella species like C. cytherea or C. nigra - I'd have to take a closer look to narrow down the species for sure, but Chlorodiella species are generally about as reef-safe as emerald crabs:

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).

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.