What is this?

[reefer2011]

What is the round thing peeking out from behind the rock? Some sort of sponge maybe? It doesn't move, has been getting bigger and the when I poke at it it feels like the outside is squishy but the inside is harder. It looks like it has extensions or hairs that come off of it. Any clue?

 

[yesjenks]

Looks like a pineapple sponge.

 

[reefer2011]

Looks like a pineapple sponge.

Can pineapple sponges get that big? It's about 1/2" by 3/4". I also don't see any holes on it anywhere. It doesn't look porous like a sponge. I wish I knew what it was.

 

[Oreo4891]

When I had an explosion of "pineapple sponges" I had one of those lodged in my sump. It seemed like it was the source, not sure if that's how they work but I got rid of it and the sponge population declined.