Spider Web?

[Cjx0r]

I just turned over a rock and noticed this white web looking stuff.

Has anyone seen this before and could ID?

 

[mcgyvr]

sponge more than likely..

 

[C.Eymann]

sponge more than likely..

+1
Maybe from the genus clathrina

 

[sil40sx]

I have tons of those at the back of my rock. Are these beneficial, or needs to be removed?

 

[SeaCucumberFan]

Beneficial. Great filter feeders