Fragilariforma meireana Van de Vijver & D. M. Williams, 2025

Fragilariforma meireana Van de Vijver & D. M. Williams sp. nov.

Figs 1 View Figure 1 , 2 View Figure 2 , 3 View Figure 3

Holotype.

BR-4867 (Meise Botanic Garden, Belgium). Fig. 1 B View Figure 1 represents the holotype .

Isotype.

Slide 453 (University of Antwerp, Belgium).

Registration.

http://phycobank.org/105490.

Type locality.

Unnamed pool at corner of Damse Vaart West and Noorweegse Kaai (Damme, West-Vlaanderen, Belgium), sample DAMME-6, (coll. date 26. v. 2018, leg. B. Van de Vijver).

Etymology.

This species is named in honour of Prof. Dr Patrick Meire, former head of the research group ECOBE (Department of Biology, Antwerp University, Belgium), and initiator of the biodiversity survey in Damme in 2018.

Description.

LM (Fig. 1 View Figure 1 ). Valves linear with almost parallel, straight valve margins only very slightly narrowing just before the valve apices. Apices clearly protracted, distinctly rostrate, very rarely capitate (Fig. 1 F View Figure 1 ). Valve dimensions (n = 25): length 35–100 µm, width 4–5 µm. Sternum very narrow, linear, running from apex to apex. Central area absent. Striae parallel throughout the entire valve length, becoming very weakly radiate at the apices, 22–25 in 10 µm. Occasionally, two stria diverging near the valve centre (Fig. 1 B, D, G View Figure 1 , black arrows). Rimoportula visible at both apices (Fig. 1 A, C View Figure 1 , white arrows). Internal cells large, hyaline, robust (Fig. 1 O – Q View Figure 1 ). SEM (Figs 2 View Figure 2 , 3 View Figure 3 ). Valve face flat with slightly raised virgae (Fig. 2 A, C View Figure 2 ). Striae uniseriate, composed of a series of small, rounded areolae (Fig. 2 B, C View Figure 2 ). Small marginal spines present, irregularly placed on the valve face / mantle junction (Fig. 2 B View Figure 2 ), usually on the virgae. Sternum very narrow, slightly raised (Fig. 2 B View Figure 2 ). Apical porefield large, entirely on the mantle, composed of at least 3–4 rows of round to quadratic porelli (Fig. 2 C View Figure 2 ). Rimoportula very small, externally rimmed (Fig. 2 B View Figure 2 , white arrows). Occasionally, 2 rimoportulae present at one pole (Fig. 2 C View Figure 2 , white arrows). Internally rimoportula small, weakly oblique (Fig. 2 D, E View Figure 2 , white arrows). Valvocopula very large, plain on one side and with series of pores on the other (Fig. 2 F View Figure 2 ). Copulae small, with serrated edge, bearing one row of pores (Fig. 3 C View Figure 3 ). Internal cell robust (Fig. 3 A, B View Figure 3 ), located between both valves. Valvocopula covering most of the internal cell (Fig. 3 B, E View Figure 3 , arrows). Internal cell with irregular ridged ornamentation (Fig. 3 D View Figure 3 ) on one side, plain on the other (Fig. 3 E View Figure 3 ). Occasionally, very shallow ridge present on the plain side visible as a thin line (Fig. 3 B View Figure 3 ).

Associated diatom flora and ecology.

Fragilariforma meireana has so far only been found in the small pool in Damme. The diatom flora in the pool is dominated by Eunotia bilunaris (Ehrenberg) Mills s. l. (21 % of all counted valves), Aulacoseira italica (Ehrenberg) Simonsen (19.5 %), Fragilaria campyla (Hilse) Van de Vijver et al. (17 %), Nitzschia archibaldii Lange-Bertalot (8 %) and Gomphonema utae Lange-Bertalot & Reichardt (6 %). Most of these species are known to prefer meso- to eutrophic conditions with moderate to higher electrolyte contents, circumneutral to alkaline conditions ( Lange-Bertalot et al. 2017). The presence of Eunotia bilunaris in this community is somewhat unusual as the species is mostly known to prefer oligotrophic, oligosaprobic conditions. However, it is clear that E. bilunaris as we know it today represents a complex of taxa present in different environmental conditions ( Vanormelingen et al. 2008).