Tiny mollusk? in very strange rock

[Steph]

Vestavia Hills, AL (Ordovician to Mississippian) 
I found these very odd rocks exposed by recent flooding.  i wondered about a tree root mold or burrow for the first one, but figured low chance of identifying. Just in case, I did a vinegar soak to remove more of the mud. 
 

Today, I saw a tiny little spiral shell.  Is it a fossil? (vs a modern snail that got trapped in this sediment). Any thoughts about the overall shape of the rock? 
 

Since it was found nearby, I’m including a pic of the other weird rock. I considered part of a horseshoe crab or trilobite molt, but I can think of more arguments against than for these.  Thanks for looking.  

[cngodles]

The top photos are probably a fossil gastropod. Not much else I can say other than it has a very low spire.