ID Please

[Sinsaint]

What is this thing?

It's a brownish color bubble type thing. I know it has to be alive. I watched it puff up and if there is any sudden movement or a shadow, it will shrink a little.

 

[fragaholic]

That would be a sponge, pineapple sponge if im not mistaken.

 

[Sinsaint]

Will it stay that small?

 

[fragaholic]

They don't get very big from what I have seen. I have a few that are the size of a quarter when fully expanded. Kind of ugly IMO, but friends always ask what they are when looking at my tank.