Diploneis zannii Frenguelli (1933: 415

Vouilloud, Amelia A., Sala, Silvia E. & Heguilor, Santiago, 2018, Revision of the type material of Diploneis zannii Frenguelli (Bacillariophyceae), Phytotaxa 351 (3), pp. 239-245 : 240

Diploneis zannii Frenguelli (1933: 415 , pl. IV, fig. 10) ( Figs 1–23 )

Description: LM ( Figs 1–16 ). Valves elliptic-lanceolate (length 37.5–57.5 μm, breadth 27–36 μm, L/B: 1.7–2.2). Longitudinal canals occupying 1/3 of valve width, together forming a narrow lanceolate area. Striae uniseriate, slightly radial at valve center (8–10/10 μm), strongly radial at poles (10–11/10 μm), interrupted at canals.

SEM ( Figs 17–23 ). Raphe filiform ( Figs 17–19 ) with external proximal ends straight located at bottom of a depression ( Fig. 18 ); distal ends curved in obtuse angle ( Fig. 19 ) to the same side. Longitudinal canals with one row of areolae separated from striae by conspicuous hyaline area ( Figs. 17–19 ). Externally, each alveolus opens as a uniseriate stria composed of equidistant areolae (10–12/10 μm) ( Figs 18–19 ). Internally, raphe straight, running through sunken area between longitudinal canals ( Figs 20–22 ); proximal and distal ends simple, helictoglossae slightly developed ( Figs 21–22 ). Transapical ribs straight delimiting alveoli ( Figs 20–23 ). Transapical ribs fungiform in transverse section ( Fig. 23 , arrows). Areolae open in single foramina ( Figs 21, 23 , arrowheads).

Type: — ARGENTINA. Corrientes: Itatí Rincón Lagoon, Esteros del Iberá , 28°42’00’’S ; 58°06’00’’W, J. Frenguelli, 24 February 1941 (lectotype designated here, Frenguelli Collection! 268, slide 268 (3), England Finder: N 47 (4), here illustrated as Figs 14–16 ; Isolectotype designated here: Frenguelli Collection! 268, Slides 268 (1–3, 6, 8, 15, 16).

Figures

FIGURES 1–16. Diploneis zannii, LM. Specimens from type population. Valve views showing specimen variation. Figs 1–13 = Isolectotypes (same specimens in different focus). Figs 14–16 = Lectotype (same specimen in different focus). Scale bar: 10 μm.

FIGURES 17–23. Diploneis zannii, SEM. 17–19: External valve view. 17. Whole valve.18. Detail showing central area and proximal raphe ends. 19. Detail showing valve end and distal end of raphe. 20–23. Internal valve view 20. Whole valve. 21. Detail showing valve end; note distal end of raphe, helictoglossa and round areolae of the striae (arrowheads). 22. Detail showing central area. 23. Detail of broken valve, note the fungiform section of transapical ribs (arrows) and the rounded areolae (arrowheads). Scale bars: Figs 17, 20: 10 μm; Figs 18–19, 21–23: 2 μm.