Eunotia tukanorum C.E.Wetzel & D.C.Bicudo

Fig. 7

Samples.

The cells observed from CCA 1847 and CCA 1849 have morphological characteristics that we consider to be consistent with the description of E. tukanorum as presented in Wetzel et al. (2010). We include a description of the population from D.R. Congo.

LM description.

Valves linear, arcuate with parallel margins. Ventral margins concave, dorsal margins convex. Apices slightly protracted and slightly expanded, rounded to bluntly rounded to slightly rectangular. Helictoglossae on the terminal nodules visible under LM as a small dot on the ventral margin. In girdle view, cells thin, isopolar, constricted in the middle portion. Striae parallel and equidistant, becoming radial towards the apices and always visible in LM. Valves measured in the present study (n = 18) with the following dimensions: length 19.5-31.0 µm, width 2.0-3.0 µm in the centre of the valve, and 2.5-3.0 µm at the apices. Stria density 20-22 striae per 10 µm in the centre of the valve. Valves measured from the type population (Wetzel et al. 2010) had the following dimensions: length 9-30.5 µm, width 2.5-3.5 µm in the centre of the valve, and 3.0-3.5 µm at the apices. Stria density 23-27 striae per 10 µm in the centre of the valve. Observed cells with characteristics consistent in general with the type population with the exception of the stria densities. Costa et al. (2017), however, documented a population from Brazil with lower stria density and consistent with the striae counts obtained in the present study (Table 1).

SEM description.

Externally and internally, areolae composed of small round pores (Fig. 7A), extending across the valve face and onto the mantle (Fig. 7B). Valve face bordered by small spines, especially at the apices (Fig. 7C). Raphe almost entirely restricted to the valve mantle on larger cells (Fig. 7B) and often highly reduced (Fig. 7C) although extremely variable and occasionally continuing onto the valve face at the terminal ends (Fig. 7A), more often observed in smaller cells. Valve mantle shallow and perpendicular to the valve face (Fig. 7B). Internally, raphe distally terminating onto a small helictoglossa (Fig. 7C), restricted to the valve mantle. One small rimoportula found at one end of the valve close to the centre of the apex (Fig. 7E).

Ecology.

The fishponds in which the species was found are used to farm Tilapia and Clarius . Water slowly enters the ponds to keep them full and the fish are fed. Concurrently with the collection of sample CCA 1847, the following parameters were measured: water temperature 30°C, electrical conductivity 16 µS .cm-1, dissolved oxygen concentration 0.88 mg.L-1. Parameters measured for sample CCA 1849 were: water temperature 29.9°C, electrical conductivity 16 µS .cm-1, dissolved oxygen concentration 1.81 mg.L-1.

Notes.

Wetzel et al. (2010) cite several defining characteristics for this taxon including the valve outline, weakly silicified delicate cells, hyaline striae, and thin cells in girdle view. The taxon from the D.R. Congo identified as Eunotia tukanorum and illustrated in the present study has characteristics consistent with these.