Development of reproductive organs in the ivory shell Babylonia japonica: observations from wild populations and laboratory-reared juveniles.

We histologically examined normal differentiation and development of genital tract and gonad in the ivory shell Babylonia japonica (Buccinidae) to determine whether the formation of male-type genitalia in imposex-exhibiting females mimics the normal development of male genitalia in prosobranch gastropods. We used a wild-caught 2-year-old specimen and laboratory-reared juveniles aged 0-24 months. Gonad differentiation was unclear before age 14 months, but progressed after 16 months. Both sexes had complete genital tract and mature gonad at 20 months. However, differentiation and development occurred earlier in females than in males. Development of genital tract preceded gonad differentiation. Vas deferens morphogenesis in males resembled that in imposex-exhibiting females. These findings help to understand the morphogenesis of genital tract and gonad in prosobranch gastropods and will contribute to more in-depth studies of the mode of action of organotin compounds such as TBT and TPhT in imposex development in female prosobranch gastropods.