A comparative study of imposex and genitalia malformation in two neogastropod species Hexaplex trunculus (Linnaeus, 1758) and Bolinus brandaris (Linnaeus, 1758) collected in the Gulf of Tunis was performed. Results showed that female H. trunculus exhibited
a more developed male genital tract than that observed in female B. brandaris. Imposex was quantified using five classic indices [I (%), VdLf, FPL, VDSI, and RPLI] and a new index (vas deferens length index, VDLI) based on the development degree of the vas deferens compared
to that recorded in stage 4 of VDSI. All imposex indices were significantly higher in H. trunculus than in B. brandaris, except for RPLI which was similar in the two species. Microscopic observations of the genital tract revealed the presence of malformations affecting
the penis and the vas deferens in some specimens of both species. The penis malformations were found in both sexes, while the vas deferens alterations were only observed in males. The development of triphallic penis was recorded for the first time in male H. trunculus. The development
of such malformations (imposex and genital aberrations) indicates the presence of pollutants responsible for these abnormalities in the Gulf of Tunis. The calculation of VDLI suggested that H. trunculus is more sensitive than B. brandaris to the organotin compounds
responsible for these malformations.
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