Nu ook levende Mytilopsis leucophaeata (Dreissenidae) in de Waal

The nomenclature of Mytilopsis leucophaeata is debated in favour of the maintenance of the genus Mytilopsis. After records of empty valves (Kelleher et al., 1997), live specimens of M. leucophaeata have since been found in the river Waal, a Rhine branch, near Nijmegen. The question of whether a permanent population of M. leucophaeta exists in the Rhine is supported by records of a live specimen attached to an aquatic moss ( Octodiceras fontanum) which grows on the groynes and an empty doublet to the zebra mussel. Furthermore, one specimen was also found attached to a stone in the river channel. However, the calcareous tubeworm Ficopomatus enigmaticus, which is found in the brackish Noordzeekanaal, was found attached to two empty valves of M. leucophaeata; furthermore, a skeleton of a brackish water bryozoan Conopeum seurati) was also found on one of the specimens. It is therefore concluded that the occurrence of M. leucophaeata in the Rhine is probably due to its intensive transport by ships from the harbours of Amsterdam and the Noordzeekanaal where these tubeworms and brackish water mussels coexist. The records of live specimens from the Waal are possible because M. leucophaeata can tolerate Rhine water salinity (0.2‰) for long periods of time.