crusty spider web looking thing-what is it?

[salty joe]

This thing is hard and crusty and fairly fragile. It's about 2 1/2 in diameter. The pic is greenish but this thing is white. All parts are stuck to the rock. No waving or moving parts.
Anybody know what it is?

 

[TriggerFinger]

My guess would be some type of sponge?

 

[samnaz]

Looks like the tube of a worm to me.

 

[reef lover]

If nothing comes out of it it could be dead dusters or a sponge.