What is on my Trachyphyllia

[RedSeaMark]

I picked up a beautiful trach last week and while doing my daily tank inspection I saw these little fan like things on the bottom. Can anyone ID?

 

[ISpeakForTheSeas]

They look like colonial tunicates to me - some species are incredibly invasive and may grow over and smother corals, but most kinds of tunicates are completely harmless filter-feeders.

You can keep an eye on them and scrape them off as needed, or - if you'd prefer - you can remove them now (either to get rid of them, or to put them in an easily monitored part of your tank where you can easily control any aggressive spreading).