Sponge or…?

[CedarReef]

these fleshy things have been growing on a piece of live rock that came from an lfs. The rock has only been in the tank a little over a week. They haven’t spread but appear to be getting bigger! What are they?

 

[KrisReef]

Possibly some kind of zooanthid?

 

[CedarReef]

Possibly some kind of zooanthid?

I think you’re right. Looks like there’s a mouth at the center.