Jellyfish? Folded Annularia?

[Rockpit]

I found this concretion already opened and heavily coated with dirt and minerals.  The few parts I could see poking through gave me hope something was preserved.  Now that I have cleaned it up, I am still trying to figure out whether or not the concretion contains a fossil.  It can look very different depending on the way you position it.  I see a jellyfish looking mantle but the tentacles look different from what I have seen before.  Positioned vertically, I start to lose the jellyfish and wonder if it is a partial annularia.   Or maybe it is just a lumpily split concretion.

[Rockpit]

Another angle.  The single half seems to have a diagonal line through the center.

[deutscheben]

It's intriguing!  I really feel like it's something, but what I don't know. As you said, it could be a very poorly preserved plant, or some kind of soft-bodied animal. I think an expert might need to see it in person to determine what.

[Mark Kmiecik]

I'm leaning towards Sphenophyllum that did not split quite right and has wear, and then I look at it again and it hints at other things. It may be one of the many "problematic" specimens that are fairly common to concretions from Illinois. Is this Mazon Creek material, or a nodule from near that area?

[Rockpit]

9 hours ago, Mark Kmiecik said:

I'm leaning towards Sphenophyllum that did not split quite right and has wear, and then I look at it again and it hints at other things. It may be one of the many "problematic" specimens that are fairly common to concretions from Illinois. Is this Mazon Creek material, or a nodule from near that area?

It is from the Mazonia-Braidwood fish and wildlife area.  I wondered about Sphenophyllum because of the wider kind of paddle shaped indentations in the right half of the pairs.  The straighter lines spiralling out look like annularia to me.  The blob at the top looks jellyfish. Are there ever plant and animal associations?

[Mark Kmiecik]

14 hours ago, Rockpit said:

Are there ever plant and animal associations?

Yes, but most probably as a product of deposition rather than interaction. Although quite improbable it is not impossible to have multiple specimens in the same plane in one concretion.