Circular Branching fossil

[Caverat]

Could this be a sponge? Note the radial structure and the occasional branching rods. Collected in Missouri, but location and age are unknown. Also, the specimen is sawn to 3/4" thick and the fossil doesn't extend into the sawn area! There is a lot of tiny crinoidal hash in the matrix rock. The light blue grid is one inch.

[Rockwood]

It is most likely a mold of the living space of a horn coral. 

Second choice would be a trace fossil. The more proper names escape me at the moment. 

[ScottBlooded]

Maybe a crinoid holdfast? I am not an expert so definitely wait for smart people to weigh in but when I search I find similarities to the branching nature of the “spokes” of your fossil

[Wrangellian]

Very interesting. I haven't a clue other than what has been suggested...   @Missourian