Coral ID please!

[Nixon]

Hey guys and gals. I've got my little 10G nano running and it's been going for a few months now. Everything seems to be going great except I'm seeing little black dots on my two clowns. I looked it up and it just looks like "skin irritation" from rubbing up against some coral. The only coral I see them hanging around are these ones and I have no idea what they are. Anybody know what they are and if they're harmful to my clowns? Thanks for your help!





They seem to like this one the most: