Pseudostaurosira katharinae Van de Vijver & C.E.Wetzel, 2024

Pseudostaurosira katharinae Van de Vijver & C.E.Wetzel sp. nov. ( Figs 1–17 View FIGURES 1–25 LM, 18–27 SEM)

Frustules rectangular in girdle view, solitary or in pairs ( Figs 1–2 View FIGURES 1–25 ). Ribbon-like colonies so far not observed. Valve mantle broad, with a large hyaline abvalvar part. Mantle plaques small but distinctly present on the mantle edge ( Figs 18–19 View FIGURES 1–25 ). Girdle composed of several plain, open, ligulate copulae, each bearing a thin siliceous ridge ( Figs 18–19 View FIGURES 1–25 ). Valvocopula largest, plain ( Figs 18–19 View FIGURES 1–25 ). Most copulae fracted ( Figs 18, 19 View FIGURES 1–25 & 26 View FIGURES 26–27 , arrows). Valves lanceolate to linearlanceolate in larger specimens, becoming more elliptic-lanceolate to elliptic in smallest valves ( Figs 3–17 View FIGURES 1–25 ). Valve margins convex to weakly convex, not linear. Apices broadly to cuneately rounded, rarely weakly protracted. Usually, one apex slightly depressed ( Fig. 19 View FIGURES 1–25 , white arrow). Valve dimensions (n=30): valve length 9–15 μm, valve width 3.5–4.5 μm. Sternum broad, lanceolate, max width 1.2–1.8 µm. Occasionally sternum narrow but abruptly widening forming a rounded central area ( Figs 11, 13 View FIGURES 1–25 ). Striae uniseriate, weakly radiate, irregularly shortened throughout the entire valve length, 14–16 in 10 μm, composed of 1–3 areolae on valve face ( Figs 20–22 View FIGURES 1–25 ), and 1–3 areolae on valve mantle ( Figs 18–19, 21 View FIGURES 1–25 ). Areolae at valve face/mantle junction markedly larger, decreasing in diameter towards sternum ( Figs 20–22 View FIGURES 1–25 ). Mantle areolae separated from those on valve face by relatively long spines ( Figs 22, 25 View FIGURES 1–25 ). Spines and areolae on both mantle and valve face surrounded by small siliceous papillae, arranged in circles ( Figs 21, 24 View FIGURES 1–25 ). Apical pore fields present on both apices, large, composed of several rows of pores located in linear depressions between raised small siliceous papillae ( Fig. 23 View FIGURES 1–25 ). Internally, areolae located each in a single depression covered by rounded volae ( Fig. 25 View FIGURES 1–25 ).

Type:— BELGIUM. Flanders, Province of Limburg, Maaseik, Bosbeek, sample APM 21-91, 51°5.6348’N, 5°45.894’E, coll. date 25 Jun. 2021, leg. Vlaamse Milieu maatschappij ( VMM) (holotype slide BR-4850, Fig. 5 View FIGURES 1–25 represents the holotype, isotype slide 448 in Collection University of Antwerp, Belgium).

PhycoBank registration:— http://phycobank.org/104825.

Etymology:— The new species is named after Katharina Wilfert , oldest stepdaughter of the first author.

Ecology and distribution:— Pseudostaurosira katharinae was described from a small river near Maaseik, in the northeastern part of Belgium. The type locality had an almost circumneutral pH (6.9–7.3), a moderate conductivity (> 200 µS/cm), and higher sulphate (12–30 mg /l) and nitrate levels (1.4–3.3 mg /l). The associated flora was dominated by several small-celled araphid species such as, apart from P. katharinae , also larger populations of Staurosirella marginostriata Van de Vijver & V.Peeters (in Van de Vijver et al. 2024: 142), S. stoksiana , Pseudostaurosira alvareziae and P. brevistriata . Other dominant species in the sample included Aulacoseira ambigua (Grunow in Van Heurck 1882: pl. 88, figs 12–15) Simonsen (1979: 56), A. granulata ( Ehrenberg 1843b: 415) Simonsen (1979: 58) and Navicula cryptocephala Kützing (1844: 95) , pointing to more meso-eutrophic, alkaline conditions (Lange-Bertalot et al. 2017). The species has also been found in a French lake (“ Mare à Goriaux ”) ( Figs 26 & 27 View FIGURES 26–27 ). The Mare à Goriaux, an intraforest pond, is located within the perimeter of the Regional Natural Park of the Scarpe and Escaut Plains, at the southern edge of the Raismes, St-Amand, and Wallers state forest ( Marchyllie, 1992). The pond, formed from mining subsidence caused by the exploitation of the Vicoigne and Arenberg pits, was originally a wetland due to groundwater outcrops. The exploitation of the Arenberg pit caused the most significant collapses, initially creating three ponds that merged around the 1930s to form the current Mare à Goriaux ( Marchyllie, 1992). The high mineral content of the pond’s water is largely due to SO 4 - ions (6 to 700 mg /l), Cl- ions (145 mg /l), as well as Na + ions (560 mg /l) and Ca + ions (110 mg /l).

It is likely that the species is more widespread than currently known due to confusion with similar taxa.