Alien on staghorn

[Oropher]

Please help ID this blue thing under staghorn branch. Thanks folks.

 

[Oropher]

Sorry couldn't get a closer picture.
By the look of it, is that harmful?

 

[samnaz]

Barnacle

like this?

 

[Oropher]

That black dot. It's like a crab, maybe?

 

[PicassoClown04]

Looks like a bivalve to me, I have a small bivalve on a maze coral frag. They’re both doing great! Small oyster/clam type thingamajiggy I don’t think they are harmful

 

[Oropher]

I had to find out.
After extraction, it's a tiny gorilla crab. dang it, this extraction must have been stressful for the coral.

Thanks folks anyway.