Five new freshwater species of Biremis (Bacillariophyta) from Tasmania

Five new species belonging to the diatom genus Biremis Mann et Cox (Bacillariophyta) were discovered during a study of benthic diatom communities of oligotrophic and dystrophic highland lakes from Tasmania. The morphological characteristics of the new species, Biremis tasmanica, B. hartzii, B. leeawuliana, B. osbornii, and B. clarensis are described using light and electron microscopy. All are confined to oligotrophic and slightly dystrophic waters. Biremis tasmanica is common and sometimes abundant; the other taxa are less widespread. Infrageneric differences within Biremis are mainly in valve shape, size, striation pattern, and external shape of the foramina, The critical generic characteristics, such as the distinctive arrangement of external rows of areolae and, most strikingly, the internal chambering below the areolae, seem to be less variable. Hitherto, Biremis was known only from estuarine and marine habitats. This paper shows that members of this genus also occur in purely freshwater habitats. Some previously described freshwater species, such as Pinnularia kriegeriana Krasske and P. schwabei Krasske, may also belong in this genus.