feather dusters growing on rock

[nrhk]

I have this rock in my sump..i been lighting up my fuse during night lately, and I found small purple feathers on the rock. I tried to take a picture and they closed up.

I also have white thin tubular like growth under the rock in DT. And it looks like fast spreading all over. is my tank being taken over by feather dusters?? if so how to avoid it??

 

[Major_oak01]

Also seen this in my tank. Not Sure what they are. Also curious

 

[Rob's Reef]

They are good filter feeders for the water. They won't harm anything