These things started randomly popping up all over my live rock about a month ago. Not sure what they are... look like yellow sponges but the tube mouth things are throwing me off.
After some Googling I have seen some people call them pineapple sponges but also found a reference to colonial tunicates. So you may have nailed it AdInfinitum!
I agree with AdInfinitum. Pineapple sponges have more of a distinctive crown on the top and are white. The ones you posted kook more like a tube on the top then a crown.