blue shroom invaders???

[rusty]

Have an ivasion of tese small discs on the shroome. help appreciated

[MaryHM]

Flatworms.

[kevinpo]

Yes they are flatworms that live on corals. They are harmless to the coral and will not spread to the rocks or sand. They are usually species specific, meaning that they will only live on that type coral and not on Acropora etc.
They can be killed by freshwater dipping the coral but this can be difficult if the coral is attached to a large rock that is part of your reef. I just let them be and the mushrooms have been doing fine for the last 10 years or so

HTH,
Kevin