The "Lessepsian" migration, although circumscribed to the Mediterranean Sea, represents the most significant biogeographical event worldwide. The pearl oyster Pinctada imbricata (Röding, 1798), was one of the first species to reach the Mediterranean throughout the Suez Canal, and since that moment had the opportunity to spread up to the western basin. To use the species as an experimental model in environmental studies, we analyzed the amount of haemolymph cells, characterized the haemocytes, and investigated their phagocytosis using the yeast Saccharomyces cerevisiae. Morpho-functional aspects of the haemocytes of P. imbricata have already been studied in some organisms from tropical Australian coasts (Kutchel et al., 2010), but no information is available in the literature about the haemocytes from this species in temperate waters. P. imbricata is able to adapt itself to high ranges of climatic, hydrological, and ecological conditions, which allows it to successfully settle in habitats very different from the native area. Moreover, it is tolerant of habitats characterized by polluted water. The species, reported from marine and transitional waters in the Strait of Messina (Central Mediterranean) by Giacobbe et al. (2010), is particularly abundant in the natural reserve “Laguna di Capo Peloro”. From such environment, several specimens have been collected to assay our analyses on haemocytes, according to Matozzo et al. (2016). In this respect, preliminary positive results indicate P. imbricata as a promising biomarker in natural and anthropogenic stressed environments.