White cocoons?

[latidati]

I have a 75 gal tank with 2 clowns, a vallentini and a blue tang. And the tank is about 5 months old. Just recently, I had these strange white cocoons appear all over my live rock. For the most part, they are little but the one I took in the photo is a good size, about dime size. They are oval with a little feather duster opening. Any ideas what these things are? Thanks for the help!

[puffer21]

Its a pinnaple sponge. There a filter feeder. Its a good thing

[sh0rtcake00]

+1 on the pineapple sponge

[zero26]

pineapple sponge

[PerezAF01]

Keep an eye on them. They can get out of hand if left unchecked.

[cwazy clown]

Yup to all the above, I have a ton of them, the feather dusters and pineapple sponges compete for space in prime spots haha