Morphological expression and different stages of imposex in Hexaplex trunculus (Neogastropoda: Muricidae) from tunisian coasts

Muricids are gonochoric gastropods, when exposed to the tributyltin (TBT), females start developing vas deferens and penis (imposex). The first morphological expressions of imposex are observed at low to moderate maritime traffic sites. In Hexaplex trunculus of Tunisian coasts, observations on imposex highlight 4 new early development stages (1d, 2d, 2d' and 3d). Stage Id presents a small segment of a vas deferens, observed halfway between the expected position of the future penis and the vagina. This stage progresses toward stage 2d' (portion of the vas deferens with a penis bud), or toward stage 2d (a long portion of the vas deferens) then toward 3d (incompletely formed vas deferens attached to a penis bud). The stage 3b, previously described in Hinia (Nassarius) reticulata, was also observed in H. trunculus. Stages 3d and 3b progress gradually leading to stage 4d and stage 4. In order to confirm these observations, experiments of transplantation and contamination in vivo by the TBT were carried out. The results showed that both the transplanted and the treated specimens by TBT express initially a portion of the vas deferens followed by the development of a penial bud. Therefore, additional information is given for the known classification scheme of imposex in H. trunculus and some prosobranch species.