What is this spider web coming from a rock?

[chrisw4111]

There is a 3-4 inch white string coming from the rock pictured below. It looks like a spider web. I pull it out with a baster and a few minutes later there is a new strong, just as long. This is the only rock in the tank that does this.
I've given the rock a good look, both in and out of water, and I can not see any semblance of a living thing, nor a hole that a worm or something could be hiding in, but this stuff can't be coming from the rock itself, rocks don't poop.
So what is the stringy stuff and what is making it?

 

[meowzer]

They could be vermitid snails, and are NOT bad....they are filter feeders
For some odd reason I can not get my pictures to work, so try googling vermitid snail and see if they look like that

 

[meowzer]

LOL....The pics worked!!!!! SO NVM about the google thing

 

[chrisw4111]

Yea the web in your 2nd picture looks like what this puts out. But I've never seen anything that looks like a little worm or snail in anywhere in the rock. I will keep a look out though, maybe its just very small or hiding in a hole I'm not seeing. Thanks.

 

[meowzer]

It's a tube, and the worm is inside it....the tube is hard, and is probably under something
you will rarely see the "snail" come out