What are these?

[mikimcat]

We have just set up our salt water tank and have some live rock. We have discovered some tube like things that we don't know what they are. We have looked everywhere, to no avail. Please help!

 

[FeatherDuster]

They look like abandoned rock featherduster tubes to me. You have cured liverock correct? I had similar structures on mine. They went away once I got my cleanup crew who picked them off.