Staurosirella constrictalonga , a new colony-forming araphid diatom species (Bacillariophyceae, Staurosiraceae) from France with some notes on a second rarely observed Staurosirella species

During a survey of the diatom flora in a sediment core sampled from a volcanic lake (Lac d’Issarlès), located in central France, two unusual Staurosirella species were discovered. Whereas one could be identified as Staurosirella coutelasiana, a rare species recently described from Switzerland, the second species could not be identified based on the currently available literature. The most striking feature of the latter is the formation of long, ribbon-like colonies using dendritic linking spines, a feature only rarely observed in the genus Staurosirella. Detailed light and scanning electron microscopy observations and comparison with the handful of known colony-forming Staurosirella species, justified the description of the latter taxon as a new species: Staurosirella constrictalonga. The new species is separated from the three known colony-forming species by its weakly constricted central part, the total absence of apical pore fields and the protracted, broadly rostrate apices.