The prosobranch gastropods Murex tribulus and Thais carnifera were found to exhibit imposex (growth of male parts in connection with female genital organs) in response to tributyltin (TBT) pollution. Six stages of imposex induction in T. carnifera (1-6) were distinguished and documented with SEM photographs for the first time; and compared with the
mode of imposex in M. tribulus which has only 4 stages. Sterilization in females of both species due to
imposex induction was recorded. Anatomical and histological details are given here. In late stages of imposex (i.e. 5 and 6) the genital pore of female T. carnifera is occluded by overgrowth of vas deferens tissue. This blockage of the pallial oviduct prevents the release of egg capsules and renders the female sterile. Hence, the aborted egg capsules are accumulated in the oviduct causing reproductive failure. In contrast, female M. tribulus did not show any potential for blockage of the genital pore. Histological investigation indicated that sterility in female M. tribulus is likely to be related to the failure of oogenesis where it was suppressed and supplanted by spermatogenesis. In contrast, oogenesis proceeded normally in T. carnifera even in late stages of imposex. It is concluded that imposex induction can virtually, if
not totally, eliminate all breeding activities in M. tribulus due to oogenesis depression, and in T. carnifera as a result of genital pore blockage.