New findings on the ecology and ultrastructure of Cymbella ancyli Cleve

Cymbella ancyli is a diatom species inhabiting oligotrophic lakes with a carbonate substratum. C. ancyli has a relatively wide geographic distribution and is considered to be rare in present day assemblages, while it is more common in subfossil material (particularly in the Ancylus Clay). During a comprehensive investigation on the ecology and depth distribution of benthic diatoms of Lake Tovel, C. ancyli was found to colonise stone and rock surfaces in the intermediate depth zone of the lake. The intermediate depth zone is stable, because it is not influenced by water level fluctuations, temperatures are low and nearly constant, and light is attenuated but sufficient. This niche may constitute a relict refugium for Cyrnbella ancyli. Analysis of the ultrastructure of C. ancyli revealed that apical pores were present, not only at the footpole, but also the headpole. This finding gives further support to the opinion that this taxon is closer taxonomically to Cymbella sensu lato than to Gomphocynibella.