Strange Sinusoidal Fossil Sponge? Burrow Trace fossils? (Missouri)

[Samurai]

Location: Missouri

Period: Pennsylvanian

Formation: Iola Formation (Raytown? Member)

 

Hi, I came across this odd find about a year ago from the Iola rockpile I used to hunt but never got time to post it. I at first thought it was bird poop but that was until I noticed an encrusting bryozoan on the fossil itself. These are not common occurrences from what I've noticed.

 

 

I sent this to Missourian yesterday and he noted the odd sinusoid and nonsegmented nature of the fossil. He wasn't sure but his best guess was sponge. 

 

I have not really seen anything like it

 

 

Here they are in relation to one another. I've found 3 so far in this chunk with the two largest pictured above. 

 

 

 

 

 

Edited May 7 by Samurai

[Rockwood]

Worm tube seems likely to me. They are sometimes preserved as steinkerns. The encrusted area could be a remnant of a tube. 

[TqB]

7 hours ago, Rockwood said:

Worm tube seems likely to me. They are sometimes preserved as steinkerns. The encrusted area could be a remnant of a tube. 

It won't be a serpulid worm tube; the earliest definite ones are Triassic with possible late Permian. So one of the enigmatic lookalikes maybe (microconchids etc. though it's rather large for a microconchid).
A good account of them here:

https://www.researchgate.net/publication/269704428_Written_in_stone_History_of_serpulid_polychaetes_through_time