Generalized system of imposex and reproductive failure in female gastropods of coastal waters of mainland China

We investigated the occurrence of imposex in gastropods from the coastal waters of mainland China from November 1999 to July 2004. Imposex was found in 30 species from 8 families, and was recorded in 20 species for the first time. In addition to the already known phenotypes of imposex expression in Cantharus cecillei, we also found aborted egg capsules in specimens with a split ventral channel (stage and type classification: S-6c) and various extensions of the proximal vas deferens (PVD). The PVD went up to or passed by the vaginal opening, and then it stopped or continued along the capsule gland. In imposex females, the penis shape and the development of the vas deferens were similar to those of the male of the same species. The morphological expressions of imposex showed diverse stages and types, Reproductive failure of females occurred in 13 species. The results suggest that imposex is widespread and severe in the coastal waters of China. Based on our aims of ecological and morphological significance, a typical imposex classification could be further generalized for all 30 species by adding S-6c((.)) and 2 subdivisions of the PVD. The generalized scheme was also ascertained to be valid for several morphological variations of imposex in previous work. Sterility at S6c(.) was proven to be due to the infolding of the capsule gland wall. We thus summed up 4 mechanisms of sterility (a, b, c and (.)) in females. Furthermore, it was shown that the normal structure of the male genital system also affected the morphological expressions of imposex to some degree, which we referred to as 'effect of male structure'. Finally, we put forward a general classification scheme of imposex with an integrated system of aims, criteria, stages, types (subtypes), pathways and mechanisms of imposex.