Caloneis mendosina Frenguelli, 1934

Sunesen, Ines, Tardivo Kubis, Jonas A. & Sar, Eugenia A., 2017, A re-investigation of three Frenguelli’s Caloneis taxa (Pinnulariaceae, Bacillariophyta) from Argentina, Phytotaxa 305 (3), pp. 165-178 : 170

Caloneis mendosina Frenguelli (slides of series #319 and associated unmounted material) ( Figs 1–15 , Table 1)

According to Frenguelli (1934) the nominal variety of C. mendosina and the var. minor differ by dimensions, valvar outline and stria density. The ranges of length of the valves given in the protologue were 81–190 μm for C. mendosina var. mendosina and 58–64 μm for C. mendosina var. minor . Nevertheless, in the original material we found a continuous range of valve lengths between 46 and 106 μm (n = 14) and also a continuous range of stria density between 11 and 14 striae in 10 μm (n = 14). Larger specimens as those described by Frenguelli were not found in the analyzed material and the stria density was consistently higher than described by Frenguelli (1934, Table 1). All analyzed specimens showed rectangular frustules, 13–29 μm in depth (n = 9), with obliquely reinforced corners, almost always lying in girdle view ( Figs 1–5 , 10, 13 ). The valves are linear-panduriform in outline, with the central undulation narrower than the distal undulations, and broadly apiculate apices which are slightly protracted ( Figs 6–8 , 11 ). Small specimens are less panduriform, with cuneiform apices ( Fig. 9 ). Valve length 46–106 μm (n = 14), valve width 9–14 μm (n = 7). The valve face is flat, narrow, depressed in the central area and slightly raised toward the poles ( Figs 11, 12 ), merging gently into a deep mantle. The valve mantle, with a curved proximal region and a vertical distal region, is deep, much shallower near the apices, and mostly unperforated ( Figs 1–5 , 9–13 ). The overlap between valve mantles of the epivalve and hypovalve forms the figure of a clepsydra as described by Frenguelli in the protologue of the nominal variety ( Figs 2, 5 ). The central nodule is elliptical, asymmetric ( Figs 1–8 ). The axial area is lanceolate, narrow near the apices and distinctly widened toward the central area ( Figs 8 , 11, 12, 14 ). The central area is large, forming a symmetrical, broad fascia ( Figs 3–14 ). The striae are alveolate, radial throughout the valve ( Figs 6–9, 11, 12, 14 ), 11–14 in 10 μm (n = 14), and ending shortly onto the mantle ( Figs 10, 13, 15 ). The outer layer of each alveolate stria appears eroded in all found specimens and the inner ingrowths of silica are opened by an elliptical aperture located at the apical junction of valve face and mantle ( Figs 11, 12, 14, 15 , arrowheads). The raphe is filiform, with slightly curved branches deflected in the same direction as the central fissures ( Figs 8 , 9, 11, 12, 14 ). The central fissures are distantly spaced, dug out on the central area and end in expanded drop-like pores, and weakly unilaterally bended toward one margin of the valve ( Figs 6–8 , 11, 12, 14 ). The terminal raphe fissures on the external face are deflected in the same direction, as a continuous arch to one side of the apex finishing close to the valve margin ( Figs 14, 15 ). The girdle bands were absent in the analyzed material ( Figs 9–15 ), possibly due to the oxidizing treatment. Taking into account the continuous range of size and stria density, and the ultrastructural similarities between smallest and largest specimens, we consider both taxa to be conspecific. Thus, we recommend that Caloneis mendosina var. minor should be considered a heterotypic synonym with Caloneis mendosina .

Figures

FIGURES 1–8. Caloneis mendosina Frenguelli (emend. Sar & Sunesen) from syntype material of C. mendosina and C. mendosina var. minor. LM. 3, 4, 7, 8, Lectotype slide. Figs 1–5. Frustules in girdle view, note obliquely reinforced corners. Figs 6–8. Valves linearpanduriform in outline. Note broad fascia and radiate striation throughout the valve. Scale bars: 10 μm.

FIGURES 9–15. Caloneis mendosina Frenguelli (emend. Sar & Sunesen) from unmounted syntype material of C. mendosina and C. mendosina var. minor. SEM. Arrowheads show the internal aperture of the alveolate areolae. Fig. 9. Small tilted frustule showing broad fascia, radiate striae and deep mantle shallower near the apices. Fig. 10. Frustule in girdle view. Note girdle bands are missing. Fig. 11. Frustule tilted showing the valve view of the hypovalve. Fig. 12. Frustule tilted showing the epivalve. Note valve surface curved proximal region and vertical distal unperforated region of the mantle. Internal elliptical apertures are located at the junction of the valve face and mantle (arrowheads). Fig. 13. Frustule in girdle view. Note alveolate striae continuing shortly onto the valve mantle. Fig. 14. Frustule tilted showing the hypovalve and the mantle of the epivalve. Note excavated raphe fissures bent toward the margin of the valve in the same direction with terminal raphe fissure. Fig. 15. Detail of the polar region of a frustule in girdle view showing terminal raphe fissure finished near the valve margin (arrows). Scale bar: 10 μm in Figs 9–14; 5 μm in Fig. 15.