Parasite on Acropora, Filter Feeder?

[Xefan]

Hi, I have these two parasites on an Acropora, they look like filter feeders of some kind, the mouths can be seen actively opening and closing on them, and reacting if I move close. Does anyone know what they are? Are they harmful for my tank? If so, how should I remove them?

Whatever they are survived Polyplab Reef Primer, Revive, and Milbemycin.

Thanks!

 

[Tahoe61]

Barnacles. Their presence on corals never concerned me.