Mediterranean Mussel Mytilus galloprovincialis Lamark, 1819 (Bivalvia: Mytilidae) Shell Damage Caused by the Invasive Polydora websteri Hartman, 1943 (Polychaeta: Spionidae) in the Gulf of Odesa, Black Sea, Ukraine

The oyster mudworm Polydora websteri is an Asian polydorid polychaete that has become invasive in different parts of Europe. Here, we provide the first report of the species parasitising Mediterranean mussels (Mytilus galloprovincialis) from the Gulf of Odesa, Black Sea, Ukraine. The P. websteri are identical in morphology to worms from the Romanian Black Sea coast and also match the original description of the species. High prevalence parameters indicate a high level of infestation in bottom-dwelling molluscs and suggests the species has spread throughout the North-Western Black Sea M. galloprovincialis population. The data suggest that the polychaetes prefer larger M. galloprovincialis (70−80 mm) with more convex and rounded valves.