Planktonic needle-shaped Nitzschia species from Lake Victoria, Africa, revisited

Abstract

Thin needle-shaped species of Nitzschia Hassall were found to form a key component of the diatom plankton in the deep Kenyan waters of Lake Victoria. An attempt was made to classify the six most common Nitzschia species of this growth form type on the basis of morphology, although they exhibit only small differences. Nitzschia lacustris Hustedt, previously described from Lake Victoria, was confirmed and recorded as an essential element of the phytoplankton. Three species were close to N. bacata Hustedt, N. graciliformis Lange-Bertalot & Simonsen and N. nyassensis O. Müller, but could not be definitively identified due to specific morphological deviations from the original descriptions, such as the overall size range, striation density and valve outline. Nitzschia bacata and N. nyassensis have repeatedly been recorded from the East African Great Lakes. Two more taxa are proposed as new to science, N. kavirondoensis sp. nov. and N. rusingae sp. nov., since neither could be matched to descriptions of the existing nitzschielloid taxa around N. acicularis (Kützing) W. Smith. Their morphological features were documented by light and scanning electron microscopy and differentiated from similar taxa recorded from Africa and other parts of the world.