Eunotia magnaparva J.C.Taylor & Cocquyt, 2024

Taylor, Jonathan C., Cocquyt, Christine & Walsh, Gina, 2024, Tropical African diatoms from the Eunotia asterionelloides (Bacillariophyta) species complex, with descriptions of new species, Plant Ecology and Evolution 157 (1), pp. 88-99 : 88

Eunotia magnaparva J.C.Taylor & Cocquyt sp. nov.

Figs 1 , 2 , 3 , 4

Type.

D.R. CONGO • Province of Équateur, Bonkele River, between Bamania and Ilenge near Eala ; 0°00 ’06.0” N, 18°20 ’57.0” E; sample CCA 4521; holotype: BR, slide BR 4755, the valve representing the type is illustrated in Fig. 1Y ; isotype: SANDC, slide SANDC-23-154 .

LM description.

Valves linear, arcuate, with considerable morphological variance over cell cycle. Ventral margins convex, dorsal margins concave. Apices distinctly capitate in large cells, subcapitate in smaller cells, bluntly rounded in the smallest cells. Apices rounded to weakly cordiform, slightly asymmetrical, expanded ventrally, indented forming a cleft in larger cells. Terminal nodule barely visible. In girdle view cells weakly heteropolar, often exhibiting some degree of flexing around the apical axis. Larger cells constricted mid-valve. Valve length 8.5-40.0 µm, width 2.0-4.0 µm in the middle, and 2.5-8.0 µm at the poles. Striae visible under LM, 16-24 in 10 µm. Striae interrupted at various points around the mid region on the apical axis of the valve, especially near to the apices in larger cells but throughout the valve in smaller cells.

SEM description.

Striae uniseriate externally and internally, composed of round areolae, occluded externally by hymenes (Fig. 3D ). Striae continuing onto valve mantle near the apices becoming discontinuous and offset near the centre of the valve (Fig. 2C ). Externally striae interrupted at the margin by a slightly thickened silica ridge. Small, conical marginal spines present in some cells (Fig. 2A, B ), especially prominent at the valve apex (Fig. 2A ), sometimes reduced and barely visible or absent on smaller cells (Fig. 2D ). Striae evenly spaced, parallel at the centre of the valve becoming radial at the apices (Fig. 3C ). Raphe slits visible externally and internally, sometimes extending onto the valve face and terminating very close to the valve apices (Fig. 3D ). Raphe slit often, though not always, greatly reduced externally in larger cells (Fig. 3B ). Valve mantle shallow, at 90° to the valve face. Internally, terminal raphe branches terminating onto small, rather elongated but well-defined helictoglossae in smaller cells (Fig. 4D, E ), absent in larger cells (Fig. 4F ). Girdle bands open with one row of occluded areolae (Fig. 4B, C ). One rimoportula present on each valve, always located close to the terminal raphe ending at the ventral part of one of the apices (Fig. 4F ).

Distribution.

The herbarium sheets sampled for diatom investigation (CCA 4510, 4511, 4521) on which Eunotia magnaparva sp. nov. was observed all came from the region around Eala, in the Province of Équateur, D.R. Congo. So far, this taxon was not observed in other materials from D.R. Congo.

Ecology.

This species was found on Utricularia and Nymphaea lotus . No further data was collected at the time of sampling.

Etymology.

The epithet Eunotia magnaparva refers to the variability of this species in terms of size over the cell cycle, magna being large and parva small, reflecting that the cells range from particularly small to comparatively large.

Registration.

http://phycobank.org/104056

Notes.

The diminution series as presented in Fig. 1 shows a notable degree of difference in the cell morphology over the cell cycle. These differences are apparent in the shape of the apices, the cell length to breadth ratio, as well as in the structure of the raphe. The width of the cells dramatically decreases with an increase in cell length. In larger cells the raphe may be highly reduced and only present at the junction of the valve face and mantle (Fig. 3A, B ), while in smaller cells the raphe is longer and extends onto the valve face (Fig. 2D ).

Figures

Figure 1. Eunotia magnaparva sp. nov., LM from type material, sample CCA 4521. Type represented by Fig. 1 Y. A - AO. Size diminution series, valve view. AP - AS. Girdle view. Scale bar = 10 µm.

Figure 2. Eunotia magnaparva sp. nov., SEM from type material, sample CCA 4521. A. External valve view of larger cell, note the cordiform apices with discontinuous striae. B - C. External valve view of cells medium size, note the reduced raphe in C and the slightly more pronounced raphe in D. Similarly, valve B has marginal spines while in valve C spines are almost absent. D. Cell representing the smallest extremity of the cell cycle, note pronounced raphe endings extending onto the valve face and interrupted striae. Scale bars = 2 µm.

Figure 3. Eunotia magnaparva sp. nov., SEM from type material, sample CCA 4521. A-C. External view of valve apices showing pattern of striation, the highly reduced raphe structure and the discontinuous striae both at the apices in A and through the cell in B. B. External valve view, note the reduced raphe (arrowhead). C. Note the external opening of the rimoportula (arrowhead). D. External valve view showing areolae occluded by hymenes, note the discontinuous striae. Scale bars = 2 µm.

Figure 4. Eunotia magnaparva sp. nov., SEM from type material, sample CCA 4521. A - F. Internal view of valve showing the internally unoccluded areolae, striae discontinuous over the valve face. D. Structure of the raphe (arrowhead), terminating in a somewhat reduced helictoglossa. F. Highly reduced raphe (white arrowhead), rimoportula present near the ventral side (black arrowhead). Scale bars = 2 µm.