Please ID

[Wiggie]

Are they reef safe?

 

[Foundry]

Nope.

These look like some branch of the Xanthid crab, a predatory hitch hiker. They can be disruptive to a reed system and munch on fish while they sleep.

We trapped and removed 2 from our tank after initial setup, they found they're way in on some LR no doubt.

 

[Sugar Magnolia]

Definitely not safe. If you have a sump put them in there.

 

[mattgumaer]

Not sure. Crabs are tough to ID a lot of the time. I think people tend to go by generalities, pointed claws=bad, more rounded=good, hairy=bad, etc.. I think the issue is that there are tons of different species of crabs and only a handful we routinely talk about in the hobby. So, it may not be possible to specifically ID them. If you have a sump, you could throw them in there. Otherwise, it's may be a question of risk tolerance.

I had a 90 gallon tank where I literally saw a crab waving around a still living fish by its tattered tail. I was able to remove the crab during a tank upgrade project.

If I were you, I'd either sump them or get rid of them. At a minimum, it's likely they're at least potentially bad actors and getting them out of a reef tank can prove to be a challenge.

Matt