Miliolid (calcareous imperforated test) foraminifera have large diffusion all over the world in a wide range of marine environments, but their distributional pattern in relation to heavy metal pollution is not clearly understood yet. The aim of this study was to better understand the biological response of the miliolid species Pseudotriloculina rotunda to experimental chronic exposure at several zinc concentrations. The duration of the experiment was 10 weeks, and six different concentrations of zinc were tested between 0 and 100 mg/L. Increasing zinc concentrations led to increasing delay or to complete cease of the new chambers’ construction, with consequences on growth rates and affected vitality and biomass variations at medium to high concentrations. Moreover, our results showed that, even at high concentrations, zinc did not cause macroscopic test deformities due to anomalous arrangements of chambers.