A comparative study of the three gastropod species Nucella lapillus (L
.), Ocenebra erinacea (L.) and Hinia (Nassarius) reticulata (L.) revea
ls that Nuccella is the most TBT sensitive species while Hinia is the
least sensitive. Of the two imposer indices VDSI and RPSI, good inters
pecies correlations were obtained only for VDSI. The three species can
be considered as complementary not only in terms of their ecology but
also for their levels of sensitivity. Indeed, Nucella and Ocenebra ar
e useful test species at TBT concentrations below 2 ng Sn l(-1) while
Hinia is the more appropriate species at higher TBT levels. For the fi
rst time, two sterilised Hinia females are recorded. This sterilizatio
n does not seem to be due to proliferation of vas deferens tissue in t
he vaginal opening and further investigation is needed to find interme
diary VDS stages between stage 4(+) and sterilization. Studies using N
ucella show that the use of narcotization in imposer analysis leads to
an underestimation of RPSI compared with non-narcotization methods. I
ndeed, narcotization straightens the penis and increases its length wh
en compared with non-narcotized animals, but this increase is proporti
onally higher in males than in females.