Pseudictyota plana (A. Schmidt) P.A. Sims & D. M. Williams, 2018

Sims, Pat A., Williams, David M. & Ashworth, Matt, 2018, Examination of type specimens for the genera Odontella and Zygoceros (Bacillariophyceae) with evidence for the new family Odontellaceae and a description of three new genera, Phytotaxa 382 (1), pp. 1-56 : 35

Pseudictyota plana (A. Schmidt) P.A. Sims & D. M. Williams , comb. nov. ( Figs 122–128 )

Basionym: Biddulphia plana A. Schmidt (1888 : pl.121, fig. 7)

Synonym: Odontella plana (A. Schmidt) De Toni (1894: 869)

Type:— “Ngucy (Weissfl.), die ganze Schale in fast gleichem Focus…” ( Schmidt 1888: pl. 121, fig. 7, figure legend)

Valves bipolar with narrowly rounded apices ( Figs 122–124 ), length 50–125μm, breadth 30–70μm. Valve face convex with rounded mantle, a barely raised ocellus at each pole and a narrow, hyaline expanded valve margin with raised border ( Fig. 125 ). Irregular network of false pseudoloculi cover valve face and mantle with 2–2.5 false pseudoloculi in 10μm at valve centre, up to 4 on mantle. Basal rows of poroid areolae meet at central line (seen on valve interior, Fig. 123 ), those at apices radially aligned. Areolae occluded by raised cribra, specialised pore present in most false pseudoloculi ( Figs 126, 128 ). Specialised pore with 5–11Y-shaped attachment points linked to form central circle ( Fig. 126 , arrow). Rimoportulae 2 (occasionally 3) positioned on valve face beneath ocellus, exterior opening through short buttressed tube, interior a slit across papillus. Valvocopula split, with substantial pars interior bordered by a ring of elongate poroid areolae occluded by sunken cribra.

Observations: —This description is based on specimens from Port Shepstone, Natal, South Africa.

A triangular form with rounded apices and gently convex margins (length of margin 60–84μm) appears in the same sample from Port Shepstone, Natal ( Fig. 127 ).

Figures

FIGURES 122–128. Pseudictyota plana (A. Schmidt) P.A. Sims & D.M. Williams (Port Shepstone, Natal, South Africa). Fig. 122. Exterior bipolar valve with barely raised elevations at apices and irregular network of false pseudoloculi covering valve face and mantle; scale bar = 10 μm. Fig. 123. Interior with attached valvocopula, transapically aligned uninterrupted rows of poroid areolae becoming radially aligned at apices meeting a short central sternum; scale bar = 10 μm. Fig.124.. Reproduction of pl. 121, fig. 7 for Biddulphia plana A.Schmidt (1888). Fig. 125. Ocellus at summit of elevation with buttressed opening of rimoportula at base; scale bar = 10 μm. Fig. 126. Irregular pattern of false pseudoloculi, basal poroid areolae mostly occluded by cribra with a specialised pore (arrow) in most sectors; scale bar = 2 μm. Fig. 127. Tripolar valve exterior with irregular arrangement of false pseudoloculi and barely raised elevation with rimmed ocellus at apices; scale bar = 10 μm. Fig.128.False pseudoloculi with basal layer of poroid areolae mostly occluded by cribra with occasional specialised pore; scale bar = 1 μm.