ID please - sponge? tunicate?

[spiraling]

I have several of these growing in my tank. Its hard, grows on the rock, and has a bunch of tubes like a colony. The tubes each have a tiny filter feeder with two 'feathers' for a cap but they are small so I could be wrong. The cap doesn't look like my tiny single filter feeders though.

Is it good or bad?

 

[frisbee]

Spionid worms?

http://www.coralpedia.com/index.php?module=Gallery2&g2_itemId=384

 

[spiraling]

hmm. I don't think so
http://www.melevsreef.com/critters/spionid-worm
The ones listed don't seem to grow in colonies and their tube is made of sand and secretion. Mine look calciferous.


hydroid was another thought, but they don't have the full crown I've seen in pictures. While they are spreading and I have them in at least 3 spots now, they are not spreading very fast.

 

[nanoreefing4fun]

The tubes each have a tiny filter feeder with two 'feathers' for a cap

maybe a type of tube worms - many types...

here is one example:

 

[spiraling]

maybe a type of tube worms - many types...

That's a definite maybe. Anyway to ID tube worms for certain?
Which I then am assuming is a good thing in the tank?

 

[Oxylebius]

Those look to be feather duster worms. Look here for lots of info on them:
Part I: http://www.wetwebmedia.com/feather.htm
Part II: http://www.wetwebmedia.com/FeatherWrmII.htm
Part III: http://www.wetwebmedia.com/FeatherWrmIII.htm
Part IV: http://www.wetwebmedia.com/FeatherWrmIV.htm