Zebra Mussel

Zebra Mussel (Dreissena polymorpha) vs Quagga Mussel (Dreissena rostriformis bugensis). The only two dreissenid mussels known to have been introduced into the US. Both the quagga mussel and zebra mussel are prolific breeders possibly contributing to their spread and abundance. The introduction of both dreissenid species into the Great Lakes appears to be the result of ballast water discharge from transoceanic ships that were carrying veligers, juveniles, or adult mussels.