We contrast ecological and life history traits of the well studied freshwater invader, the zebra mussel (Dreissena polymorpha), with the lesser known invasive golden mussel (Limnoperna fortunei) to compare salient biological traits and environmental limits, and to predict the potential spread and ecosystem impacts of L. fortunei in areas where it is introduced. Both species are sessile, byssate bivalves with a planktonic larval stage and extremely high reproductive capacity. For both species adults attain much higher biomass in waterbodies they invade than all of the native invertebrates combined, and they create substrate complexity otherwise not found in freshwater systems. Both are very active suspension feeders, greatly enhance benthic-pelagic coupling, and act as effective ecosystem engineers. Although taxonomically unrelated, their ecosystem impacts are surprisingly similar and follow from the novel ecological niche they share, rather than being species specific. The golden mussel has broader environmental tolerances and therefore may be a much more successful invader than D. polymorpha in regions dominated by acidic, soft and contaminated waters. In the near future L. fortunei may colonize the southern and central parts of North America, much farther north than has been previously predicted. Although to date the zebra mussel is considered the most aggressive freshwater invader, soon many waterbodies may receive another, even more aggressive invader.