Thalassiosira gessneri Hustedt and T. lacustris (Grunow) Hasle in the rivers Moselle (Luxembourg), Rhône, Saône (France), Danube (Hungary) and the channel Main-Danube (Germany)

Abstract

Since the description of Thalassiosira gessneri by HUSTEDT (1956) from the lake Maracaibo (Venezuela), only HASLE & LANGE (1989) published an important paper on this centric diatom from five rivers of USA. During the present study twenty-two centric diatom taxa were found in the phytoplanktron samples of the Luxembourgish stretch of the river Moselle. Several of them are relatively common in European rivers but some of them are rare or interesting in morphological and/or taxonomical point of view: Actino-cyclus normanii (GREGORY) HUSTEDT, Cyclotella scaldensis MUYLAERT et SABBE, Thalassiosira gessneri HUSTEDT, T. incerta MAKAROVA. The discovery of the brackish water species Thalassiosira gessneri in the phytoplankton of the River Moselle seems to be one of the first records from Europe. We also recently found it in periphyton samples of the rivers Rhone, Saone in France near Lyon and in the phytoplankton of River Danube in Hungary near Dunakiliti, of Main-Danube Channel in Germany at Kelheim. A morphological comparison was made, in light- and scanning electron microscope, of specimens from the lake Maracaibo, from North American rivers (HASLE & LANGE, 1989) and European rivers. A detailed morphological analysis of T. gessneri and T. lacustris is given, in comparison with related taxa: T. australiensis (GRUNOW) HASLE and T. bramaputrae (EHRENBERG) HAKANSSON. A discussion about the nomenclatural position of T. lacustris (GRUNOW) HASLE is also presented.