Two new species of Nanofrustulum (Bacillariophyta) from temporary rivers in the Alentejo region, southern Portugal

Two new Nanofrustulum species, N. lucectorii sp. nov. and N. ibericum sp. nov. are described from temporary streams in southern Portugal based on light and electron microscopy observations. Nanofrustulum lucectorii sp. nov. is characterised by elliptic valves with broadly rounded apices, spines with a solid core, an apically elliptic base, a flattened body, and spatulate, serrate tips that are wider than the spine body. These spines have rectangular stipules covering the first subtending mantle areola. The equal apical pore fields are present at both valve apices and are composed of a single transapical row of sunken pores. Nanofrustulum ibericum sp. nov., in turn, is unique in that it has solid spines with a triangular or trapezoid base, and a triangular and recurved body. Additionally, the blisters on the abvalvar side of the mantle are pervalvary rectangular and widely spaced. The morphological features, ecology and distribution of the new species are discussed based on relevant literature.