Nanofrustulum cataractarum (Hustedt) C.E. Wetzel, E. Morales & Ector in Morales et al. 2019b, Plant Ecology and Evolution 152, p. 275.

Morales, Eduardo A., Wetzel, Carlos E. & Ector, Luc, 2021, New and poorly known " araphid " diatom species (Bacillariophyta) from regions near Lake Titicaca, South America and a discussion on the continued use of morphological characters in " araphid " diatom taxonomy, PhytoKeys 187, pp. 23-70 : 23

Nanofrustulum cataractarum (Hustedt) C.E. Wetzel, E. Morales & Ector in Morales et al. 2019b, Plant Ecology and Evolution 152, p. 275.

Figs 1A-E (LM), 2A, B (SEM)

Basionym.

Melosira cataractarum Hustedt 1938, Archiv für Hydrobiologie, Supplement 15, p. 142, pl. 9, figs 6-7.

Most current illustrations of type material: Wetzel et al. 2013a, figs 1A-AB, 2A-G; Beauger et al. 2019, figs 93, 94.

Synonym.

Pseudostaurosira cataractarum (Hustedt) C.E. Wetzel, E. Morales & Ector in Wetzel et al. 2013a Acta Nova 6(1-2), p. 60.

Comment.

The taxon was first described for insular Asia, specifically from Java, Indonesia, by Hustedt (1938). Type material was reanalyzed by Wetzel et al. (2013a) and Beauger et al. (2019) and regional and worldwide distributions were presented in Wetzel et al. (2013a) and Grana et al. (2015).

As presented in Table 2 in Grana et al. (2015), N. cataractarum from Bolivia (Figs 1A-E , 2A, B ) are smaller (length and width: 4.5-5 µm) than specimens in Asian type material (length 5.8-8.2, width 5.4-7.2), and the stria density of the Bolivian population is higher than that from Asia (18-20 and 15-28 in 10 µm, respectively). Regarding the areola density there is a complete overlap between both populations (2.5-3.5 in Bolivian specimens and 1-4 per 1 µm in Asian ones). Other features, such as the pattern of areolation in both valve face and mantle, the ample, round to oval axial area, the round to slightly elongated base and flattened body of the spines with small lateral projections, are similar in both populations. Also, the depression into which the areolae from valve face and mantle open internally is similar in Bolivian and Asian specimens (Fig. 2B ). The features of the girdle elements with short but wide body and prominent ligula is also comparable in both populations. The Bolivian specimens tended to have more prominent blister depositions at the abvalvar edge of the mantle (Fig. 2B ). All populations reported from around the world lack apical pore fields, and areolae flaps or spine stipules have not been reported either.

Taking into account all the above-mentioned reports, the dimensions for this taxon are length: 2.8-8.2 µm; width: 2.7-7.2; stria density: 15-29 in 10 µm; areola density: 1-4 in 10 µm.

In Bolivia, the taxon has been found in the Desaguadero and Sajama rivers. Fig. 2A is the first illustration of the taxon for the Desaguadero River.

Figures

Figure 1. A-M ' LM images of little known and new " araphid " diatoms from the Bolivian Altiplano A-E Nanofrustulum cataractarum F-L N. rarissimum M-S Pseudostaurosira sajamaensis T-Z P. pulchra sp. nov. (Fig. 1 U is the holotype) A' - G ' P. aedes sp. nov. (Fig. 1 A ' is the holotype). H' - M ' P. heteropolaris sp. nov. (Fig. 1 I ' is the holotype). Scale bar: 10 µm.

Figure 2. A-F SEM images of little known " araphid " diatoms from the Bolivian Altiplano A, B Nanofrustulum cataractarum A specimen from the Desaguadero River, showing quasifract girdle elements with prominent ligulae (white arrows) B specimen from the Sajama River showing common internal depression into which the areolae open (dotted arrows) and the blister-like depositions of silica at the abvalvar edge of the mantle C, D N. rarissimum from the Desaguadero River C small, spineless valve D internal view showing apical and foot pole pore fields (black arrows) and internal depressions containing all areolae within a stria (dotted arrow) E, F Pseudostaurosira sajamaensis from the Desaguadero River E top view showing gradual transition of valve face to mantle and the reduced apical pore fields (black arrow) F side view of two half cells still attached by heavily silicified spines. Notice open girdle elements (white arrows). Scale bars: 1 µm (B); 3 µm (C, E); 4 µm (A, D); 5 µm (F).