(Ile8)-Oxytocin is a neurohypophysial hormone mesotocin produced in marsupials[1].
References
[1] Chauvet MT, et al. A reptilian neurohypophysial hormone, mesotocin (Ile8-Oxytocin), in Australian marsupials. FEBS Lett. 1981 Jun 29;129(1):120-2. DOI:10.1016/0014-5793(81)80770-3