Is this a sponge or just a porous chunk of limestone?

[Addish]

I’m not exactly sure where it comes from but I found it in paved gravel in association with chert that likely came from the Knox Group in Northeast Alabama. 

[Ludwigia]

Hard to tell from the indistinct photos, but the wonky form doesn't point to sponge and I can see no signs of ornamentation that one would expect from one on the surface.