Eunotia tropicaesilvae Cocquyt & J.C.Taylor, 2025

Eunotia tropicaesilvae Cocquyt & J.C.Taylor sp. nov. (LM: Figs 1–42 View FIGURES 1–42 ; SEM; Figs 43–54 View FIGURES 43–50 View FIGURES 51–54 )

Description LM: — Frustule in girdle view broadly rectangular, copulae on dorsal side considerably narrower than on the ventral side, both valve faces obliquely visible from the dorsal side. Silica thickenings present on the valve mantle at the junction with the copulae. Valves dorsiventral. Ventral valve margin of longer cells straight, ventral margin of smaller specimens evenly convex; strongly convex dorsal margin. Ends obliquely protracted, sub-rostrate to rostrate, in larger cells strongly dorsally deflected. Ends in most cells heteropolar. Length 12–36(46) μm, breadth 4.5–7.0(8.0) μm. Terminal nodules close to the poles in shorter cells, further away in larger specimens. Terminal raphe fissures short to very short on the valve face, in some cases entirely on the valve mantle. Striae more widely spaced in the centre of the cell, weakly radial, 9–14 but mostly 10–12 in 10 μm, becoming denser and sometimes less prominently radial near the apices, 14–16 in 10 μm. Areolae not resolvable in LM.

SEM:— Externally terminal fissures slightly enlarged, mostly restricted to the mantle ( Fig. 43 View FIGURES 43–50 ) occasionally extending onto the valve face ( Fig. 46 View FIGURES 43–50 ). Internally the raphe fissures terminate, only moderately bent, in raised helictoglossae ( Figs 52–54 View FIGURES 51–54 ). Raphe fissures end in a rather large terminal nodule which extends as a hyaline area free of striae to the dorsal margin ( Fig. 52 View FIGURES 51–54 ), and to the edge of the mantle ( Fig. 44 View FIGURES 43–50 ). Striae uniseriate, interrupted at the junction of the valve face and mantle on the ventral margin by a marginal crest ( Fig. 45 View FIGURES 43–50 ). Marginal ridges, formed by virgae resulting from indented striae, are present on the dorsal margin visible in both LM ( Fig. 14 View FIGURES 1–42 ) and SEM ( Fig. 49 View FIGURES 43–50 ). Areolae (35) 40–45 in 10 μm, with small foramina lips ( Figs 48, 49 View FIGURES 43–50 ). Dense concentrations of areolae present on both poles forming striae perpendicular to the apical pole ( Fig. 47 View FIGURES 43–50 ) often somewhat irregularly arranged ( Fig. 49 View FIGURES 43–50 ), consistent with apical pore fields. Spines absent from the poles and valve margins. A single rimoportula is present located on the valve mantle almost directly in line with the terminal fissure ( Fig. 52 View FIGURES 51–54 ). A pseudoseptum-like structure may be observed at the apices in both LM and SEM ( Figs 51, 53 View FIGURES 51–54 ). Several girdle bands present. Valvocopula thin and not perforated. At least one short, open band near the apices broader on the ventral than on the dorsal side, and one broader, probably closed band with a transapical row of areolae, 30 in 10 µm, near both edges and irregularly scattered areolae in-between.

Type:— DEMOCRATIC REPUBLIC OF THE CONGO. Tshopo Province : Moni River , just downstream from the campsite in the tropical rain forest, sand from the stream bed, 0°50’47.29”N and 24°32’36.63”E, CCA 4386 View Materials , Andreas Popelier , 18 July 2017 (holotype BR! 4846, Meise Botanic Garden, Belgium, the valve representing the holotype is here illustrated in Fig. 21 View FIGURES 1–42 ; isotype SANDC! 24-538, South African National Diatom Collection, South Africa) GoogleMaps .

Registration:— http.//phyocbank.org/105517

Etymology:— We name this new Eunotia species after the tropical forest habitat in which it occurs.

Ecology and distribution:— The species was found in streams in the tropical rain forest with sandy substrate, with a pH ranging from 5.33 to 5.71 and conductivity ranging from 9.8 to 12.7 µS. cm-1. Measured nitrate values ranged from 0.124 to 0.191 mg.L- 1. Besides the type locality this species was also observed in the Libongo, Isalowe and Ngima rivers, all located in the Yangambi Biosphere Reserve in the Tshopo province of the D.R. Congo. Eunotia tropicaesilvae was found at a relative abundance of 7.6% in sample CCA 4386, other taxa found in the sample included: Eunotia spp. (30%) and small Naviculoid taxa (37.4%).