Cocoons in my tank?

[neowind]

About 6 months ago I came accross a cocoon in my nano tank. It was kinda like a swirled web gel type material on my LR. I didn't think anything of it until today I looked and it has gotten kinda huge and looks like something is living in it and it has a whole on the top now kinda like an ant hill but more like a webbing or gel type material. I noticed there are 4-5 of them on my LR now. Anyone know what this is? I will try and get some pictures but I figured someone may know what it is.

 

[sabby]

Sounds kind of like a sponge or sea squirt of some kind...

 

[ekclark]

I think I know what you are talking about...I have some on my lr. It is just some sort of sponge and is harmless as far as I've noticed. It actually looks pretty cool imo.