Pseudostaurosira bardii (Fragilariaceae, Bacillariophyta), a new species from a saline hydrothermal spring of the Massif Central (France)

Light microscopy (LM) and scanning electron microscopy (SEM) observations on a new species of the genus Pseudostaurosira from a spring of the Massif Central (France) are presented. The new species, with very small dimensions, presents similarities with other species previously observed in other parts of Europe. However, based on its morphology, the new species presents striae sometimes composed of only two areolae on the valvar surface: one big, round or elliptic near the mantle edge and the second smaller, slit-like or round (sometimes completely occluded externally) situated further toward the interior. Moreover, the size, the density of striae and the presence of volae allow the separation of Pseudostaurosira bardii from the other species. Morphologically similar species were also re-investigated in the current project, including the type material of Pseudostaurosira trainorii E.Morales, Pseudostaurosiropsis connecticutensis E.Morales and Pseudostaurosira cataractarum (Hustedt) C.E.Wetzel, E.Morales and Ector. They were also investigated and illustrated using SEM. The ecological preferences of Pseudostaurosira bardii are briefly discussed.