Diatoms of Europe, Volume 9: Freshwater Diploneis: Two Studies

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This volume contains two studies:

Freshwater Diploneis: Species Diversity in the Holarctic and Spot Checks from Elsewhere:
A total of 107 Diploneis taxa is treated comprehensively in the present contribution. This includes morphological description, differential descriptions respectively, distribution, ecology and critical discussion. We describe 66 species or subspecies as new to science. For the 14 species recently introduced by Lange-Bertalot and Fuhrmann (2016, 2017) data have been amended. Several of the new species from Europe are published under a joint authorship with our colleagues E. Jovanovska and Z. Levkov who have found the same taxa independently in North Macedonia. Diploneis mereschkowskyi is the new name for a taxon that was described originally as a variety of D. smithii (Brébisson in W. Smith) Cleve and has now been promoted to species rank. In addition, numerous specimens from various locations are shown without full descriptions. Presumably they belong to as yet unknown, at any rate undescribed species and merit recording as pointers to future work.

We propose a subdivision into three subgenera: Diploneis in the sense of the type species, Cribradiploneis, and Volaediploneis. Nevertheless we recommend maintaining the genus Diploneis in its actual circumscription. This is strongly justified by the ubiquity of the H-shaped silica complex functioning as a stabilising cell skeleton in all marine and freshwater taxa of Diploneis.

The Genus Diploneis in the Republic of North Macedonia
A revision of the genus Diploneis in North Macedonia is presented here. A wide variety of aquatic habitats are studied, ranging from ancient lakes to high-elevation mountain ecosystems. Fossil data is also included from sediment records of Lake Ohrid and Lake Prespa. All taxa are analyzed with light and scanning electron microscopy, and compared with morphologically related species. For each species the distribution and the ecology are given. The studied habitats revealed 36 Diploneis species, nine of which are new to science (e.g., Diploneis affinis, D. formosa, D. neglecta, D. parvula, D. perminuta, D. permodica, D. subalpina, D. subkrammeri and D. submarginestriata). Most of the new species occur in the contemporary diatom flora, with only two species found in the sediment records of Lake Ohrid and Lake Prespa. The majority of them inhabit the ancient lakes, and only three occur in the mountain ecosystems. Here, we also describe a small Diploneis species from Lake Ohrid, which has previously been misidentified as D. petersenhi. This species also occurs in Lake Hovsgol, Mongolia.

This extensive research of species in the genus Diploneis has enhanced our knowledge of its occurrence in North Macedonia with respect to species richness and distribution and, at the same time, has improved taxonomic and nomenclatural understanding of freshwater Diploneis.

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