Is this a sponge, Duster, or Hydroid?

[dansd]

My tank is about 5 months old. These guys started to appear on my power heads about a few weeks ago. I'm guessing they are a sponge, but I'm not sure. Should I try to remove them, or are they beneficial?

Thanks,
Dan

 

[wade1]

http://www.reefs.org/phpBB2/viewtopic.php?t=63449

Just answered in this thread...