Arcanodiscus saundersianus Goeyers & Van de Vijver 2020, sp. nov.
Creators: name: Goeyers, Charlotte
name: Vijver, Bart Van De
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Chromista
Ochrophyta
Bacillariophyceae
Arcanodiscales
Arcanodiscaceae
Arcanodiscus
Arcanodiscus saundersianus

description: Arcanodiscus saundersianus Goeyers & Van de Vijver sp. nov.  http://phycobank.org/ 102320 Figs 97–115, 132–138  Etymology  
The species is named in honour of our colleague Dr Krystyna Saunders (Australian Nuclear Science and Technology Organisation, Kirrawee, Australia) to acknowledge her for her ecological and paleoecological diatom research on the sub-Antarctic islands in the Pacific Ocean.  Material examined  
 Holotype   
CAMPBELL ISLAND • sub-Antarctic region; sample BAS272; 26 Dec. 1969; D. Vitt leg.; BR-4581.  
 Isotype   
CAMPBELL ISLAND • same collection data as for holotype; slide at University of Antwerp, Belgium; PLP-372.  Description  
 Light microscopy (Figs 97–115)   
Frustules broadly discoid, almost square to rectangular with broadly rounded edges and convex valve faces. Frustules often found attached to each other. Chains composed of more than 2 cells however never observed. Multiple discoid chloroplasts present. Girdle bands not discernible in LM. Valves rather strongly silicified, rounded with a thick mantle and convex, weakly domed valve face. Valve dimensions (n = 25): valve diameter 6–17.5 μm, frustule height (n = 10): 4.5–7.0 μm. Central area is a large, smooth, hyaline zone, 3.0–7.5 μm, 50–55% of the total valve diameter, surrounded by a more rugose, irregularly shaped, marginal zone where striae are difficult to distinguish. Visible processes lacking.  
 Scanning electron microscopy (Figs 132–138)   
Frustules discoid with very heavily silicified valves, visible as a thick mantle (Figs 132, 137). Cingulum comprises several, narrow, very thin, non-perforated, open copulae (Fig. 132). Pars interior of the copulae clearly fimbriate giving the impression of perforations on the copulae when girdle not eroded (Figs 132, 133, arrows). Copulae clearly open, ligulate (Fig. 132, double arrows).  
Valve face with large, flat hyaline, clearly rounded central area, lacking areolae and any other ornamentation (Figs 134–136). Marginal zone gently sloping towards the mantle, entirely covered with rounded to slit-like areolae, ca 45 in 10 μm, organized in irregular striae, the latter ca 40 in 10 μm. Areola occlusions externally not observed (Figs 134–135). External openings of portulae not distinguishable from areola openings. No silica thickenings, close to valve face/mantle junction (Fig. 135). Striae continuing over the valve face/mantle junction, usually interrupted by a series of up to 3 parallel ridges running entirely around the mantle (Figs 134–135). Parallel ridges, usually covered by girdle bands (Fig. 133), occasionally lacking and resulting in a broad, flat mantle (Fig. 136). Areolae on the mantle strictly rounded. Mantle edge indistinct.  
Internally, areolae rather large, each showing a clear rota, covered by very thin hymenes, organized in irregularly running striae (Fig. 138). Central area a large hyaline, irregularly bordered, central zone (Fig. 137). Large number of perforated, thickened protuberances visible, irregularly scattered between the areolae, never organized in a regular marginal ring (Fig. 137, arrows). Inner openings of these protuberances rounded, smaller than the areolae, lacking rota (Fig. 138).  Ecology and distribution  
 Arcanodiscus saundersianus sp. nov. was found in a sample collected from a dripping bluff limestone. The sample is entirely dominated by the new species of Arcanodiscus. Sub-dominant species include Achnanthes muelleri, Diatomella balfouriana and several species of Humidophila.
description: Published as part of Goeyers, Charlotte & Vijver, Bart Van De, 2020, Revision of the non-marine centric diatom flora (Bacillariophyta) of the sub-Antarctic Campbell Island (southern Pacific Ocean) with the descriptions of five new species, pp. 1-30 in European Journal of Taxonomy 694 on pages 18-20, DOI: 10.5852/ejt.2020.694, http://zenodo.org/record/3973347