Abstract
A SEM study of the morphology of Naviculadicta witkowskii Lange-Bertalot & Metzeltin, found in samples from acidic lakes of Polistovo-Lowatsky Bog System (Russia), revealed that it is characterized by striae composed of alveoli occluded externally by thin closing membranes; a second row of shorter elongated slits is present on the mantle. This species also has a naviculoid raphe. All of these structures together with the shape of the valve conform to the genus Chamaepinnularia Lange-Bertalot & Krammer. The most characteristic feature of Chamaepinnularia witkowskii (Lange-Bertalot & Metzeltin) Kulikovskiy, Lange-Bertalot is the presence of a narrow lanceolate hyaline area that interrupts the striae. Only one marine species from this genus—Chamaepinnularia distantepunctata (Simonsen) Witkowski, Lange-Bertalot & Metzeltin—has a similar hyaline area. Morphological variability of this taxon, collected from the natural population, was studied. The length of valves is a more unstable characteristic than the breadth and number of striae in 10 um. Since the Eemian Interglacial, Chamaepinnularia witkowskii is known as an acidobiontic species from only humic lakes and Sphagnum bogs of Europe (France, Finland, Russia).
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