The conical hole in the legmen of a Mississippian crinoid (Macrocrinus mundulus) directly underneath the shell of a platyceratid gastropod, Platyceras (Orthonychia) sp., and similar holes in other Mississippian crinoids (Batocrinus irregularis and B. icosidactylus) demonstrate the drilling abilities of platyceratids. This is the first case of drilling by an archaeogastropod. Drilling on the crinoid host by the gastropod was non-predatory; the relationship was probably parasitic. This study, the first to identify unequivocally a Palaeozoic borer, supports the notion that gastropod drilling has evolved several times