Vas deferens and penis development in the imposex-exhibiting female rock shell, Thais clavigera

The characteristics of the development of male genitalia (penis and vas deferens) in imposex-exhibiting female rock shells, Thais clavigera, were histologically examined using specimens from a wild population and tributyltin (TBT)-exposed females in the laboratory. A variety of vas deferens morphogenesis patterns were observed in wild female T. clavigera, and the characteristics were summarized. The immature vas deferens at an initial stage, however, was only observed beneath or behind the penis, and no vas deferens was observed close to the vaginal opening (i.e., vulva) of the capsule gland in TBT-exposed females, which was different from the characteristics of vas deferens formation observed in wild females. Taking into consideration both the observed results from wild female specimens and from TBT-exposed females in the laboratory, the vas deferens sequence (VDS) index for T. clavigera was proposed as VDS 1-6.