Here is an excellent new paper with a detailed section on post-mortem feeding traces associated with trilobites:
Kraft, P., Bruthansová, J., Mikuláš, R. 2020
Feeding Traces Related to Shells from the Prague Basin, Czech Republic (Tremadocian to Early Darriwilian, Ordovician).
Palaeogeography, Palaeoclimatology, Palaeoecology, 537(109399):1-21 OPEN ACCESS PDF