Аннотация:Abstract. In the Azores the gastropod Thais haemastoma shows varying degrees of imposex, the induction of male sex characters in the female. It is inferred that imposex in T. haemastoma is caused by tributyltin (TBT) associated with boats using organotin‐based antifouling paints. The two indices ‐ relative penis size and vas deferens sequence ‐ employed previously for Nucella lapillus , were used without alteration. T. haemastoma is only the third species reported as exhibiting ‘effective sterilisation’ of the female. Unlike Nucella lapillus, T. haemastoma has a planktonic larva, allowing populations to be sustained even when local TBT pollution is high. This makes T. haemastoma potentially a better indicator species, as monitored populations can be maintained by the influx of larvae. T. haemastoma may thus provide a cheap method of assessing the extent of TBT contamination in warm waters, particularly in the Mediterranean and Atlantic Islands. Preliminary examination of material from a marina in Spain showed a high incidence of ‘sterile’ animals.
