A. Epoxy resin casts of the microboring Orthogonum giganteum Glaub, 1994, oriented closely parallel to the external substrate surface of an articulated brachiopod (sample C31). B. Close-up of A, showing the cylindrical tunnels and the characteristic rectangular branching pattern. The small ridges on the tunnel surface are a xenomorphic ornament reflecting the brachiopod’s shell microstructure.