Fossil Microscopic Encrusting Tubular Organism

These photos illustrate an unidentified mound-building organism discovered in the Carboniferous (Mississippian) of North Alabama (Haywick and others, 2016). The mounds also include some larger tubes, probably made by worms, indicated in one of the photographs. Any ideas about what made the small ones will be greatly appreciated.

 Several of the larger tubes, which we interpret as worm tubes, indicated by black and white arrows.

 Mound-building tubular organism growing off of a brachiopod spine and extending towards the center of the photograph.

Mound-building tubular organism indicated by large white arrow.

Haywick, D.W., Kopaska-Merkel, D.C., and Keyes, R., 2016, Petrographic and faunal characteristics of Monteagle and Hartselle-equivalent strata in northeast Alabama, Gulf Coast Association of Geological Societies Transactions 66, p. 211-229.