THE MORPHOLOGICAL EXPRESSION OF IMPOSEX IN NUCELLA LAPILLUS (LINNAEUS) (GASTROPODA: MURICIDAE)

The prosobranch gastropod Nucella lapillus exhibits imposex (occurrence of male parts in addition to the female genital duct) in response to tributyltin (TBT) pollution. Six stages with three different types in the first three stages and two types in the last two stages can be distinguished and are documented with SEM-photographs for the first time. Furthermore, nine additional alterations to the genital tract are shown. As a consequence of TBT exposure in early life stages a sex change might occur. The oogenesis is suppressed and supplanted by spermatogenesis. The results are two observed specimens with a male genital tract (with a testis) and different female parts. Anatomical and histological details are given here. If TBT-exposition occurs later, the vagina is replaced by a small prostate gland or the vaginal opening is occluded by proliferating tissue. The two established indices for PSH monitoring (VDS and RPS) in muricid gastropods are discussed. It is shown that the VDS is the more valid parameter.