Tracking a global invader: first detection of Helobdella europaea (Hirudinea: Glossiphoniidae) in Italian inland waters and new insights into its origin

In this study, we report the first morphologically and molecularly confirmed occurrence of the invasive leech Helobdella europaea in Italy and provide further material from Ukraine. Bayesian inference and maximum-likelihood phylogenies consistently grouped all newly obtained sequences of the mitochondrial gene cytochrome c oxidase subunit I into a well-supported H. europaea lineage, characterized by low intraclade divergence. Population genetic analyses revealed low nucleotide diversity and a significantly negative Tajima’s D, supporting a recent expansion event. Ancestral range reconstruction revealed a Nearctic origin for the species, contrasting with previous suggestions of its Neotropical provenance. These findings enhance the phylogeographic scenario of H. europaea and broaden its known distribution across the Mediterranean region.