A substantial body of evidence supports the use of extracorporeal shock wave therapy (ESWT) for fracture non-unions in human medicine. However, the success rate (i.e., radiographic union at six months after ESWT) is only approximately 75%. Detailed knowledge regarding the underlying mechanisms that induce bio-calcification after ESWT is limited. The aim of the present study was to analyse the biological response within mineralized tissue of a new invertebrate model organism, the zebra mussel