This is a rare and  Original nodule of Tullimosntrum gregarium
 
 
Tullimonstrum gregarium is an extinct genus of soft-bodied bilaterian that lived in shallow tropical coastal waters of muddy estuaries during the Pennsylvanian geological period, about 300 million years ago. A single species, T. gregarium, is known.Tullimonstrum have been found only in the Mazon Creek fossil beds of Illinois, United States. Its classification has been the subject of controversy, and interpretations of the fossil likened it to molluscs, arthropods, some type of worms and vertebrates.
we base the model reconstructions on the last publication that described tully like  a basal vertebrate, and thus a member of the phylum Chordata.
 
Tullimosntrum gregarium
Carboniferous Pennsylvanian
Mazon Creek Fossil Bed
Francis Creek Shale
Pit.?
Grundy County
Illinois
USA
 
 
 
McCoy, Victoria E.; Saupe, Erin E.; Lamsdell, James C.; et al. (April 28, 2016). "The 'Tully monster' is a vertebrate". Nature. 532 (7600): 496–499. doi:10.1038/nature16992. PMID 26982721.