What are these growing out of my rock?

[Jenny mitchell]

we have a few white tube like things growing out of our rock. At first there was just one, but are more now, should be getting rid of them?

 

[Becky]

Weird! Are they flexible or spiny? And do they retract?

 

[Jenny mitchell]

They're flexible and didn't retract when I touched one of them

 

[Big K]

Looks like some type of sponge to me. I have the same thing I believe. I'd say it's harmless.