Nanofrustulum rarissimum E. Morales, Novais, C.E. Wetzel & Ector in Morales et al. 2019b, Plant Ecology and Evolution 152, p. 269, figs 1A-K, 2A-D.

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 rarissimum E. Morales, Novais, C.E. Wetzel & Ector in Morales et al. 2019b, Plant Ecology and Evolution 152, p. 269, figs 1A-K, 2A-D.

Figs 1F-L (LM); 2C, D (SEM)

Comment.

This taxon was first described by Morales et al. (2019b) from the Desaguadero River. Here we present illustrations of specimens from the Sajama River for the first time (Fig. 1F-L ). Thus far, this diatom has only been seen in samples from these two sites.

The specimens found in the Sajama sample fit the dimensions of the type population, except for the length, with Sajama River specimens being shorter (5.1-9.7 µm). At the SEM levels, no differences were noted between specimens from both sites.

Our reanalysis of Desaguadero River material yielded small valves that are spineless (Fig. 2C ), but that had all the other features similar to those of larger, spiny specimens. Also, we were able to capture the apical and foot pole pore fields from an internal view (Fig. 2D ), confirming that both are developed, but that the one at the foot pole is larger. Additionally, we were able to confirm the raised nature of the axial area and virga in internal view (Fig. 2D ), which leaves all the areolae within a stria open into a single internal depression.

The smaller specimens found in the Sajama River sample expand the length range of this taxon which now has the following diagnostic measurements length: 5.5-9.5; width 2.5-3.3; stria density 12-13 in 10 µm.

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).