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 Author Goeyers, Charlotte Meise Botanic Garden, Research Department, Nieuwelaan 38, B- 1860 Meise, Belgium & University of Antwerp, Department of Biology, ECOBE, Universiteitsplein 1, B- 2610 Wilrijk, Antwerpen, Belgium. goeyerscharlotte@hotmail.com Author Vijver, Bart Van De Meise Botanic Garden, Research Department, Nieuwelaan 38, B- 1860 Meise, Belgium & University of Antwerp, Department of Biology, ECOBE, Universiteitsplein 1, B- 2610 Wilrijk, Antwerpen, Belgium. bart.vandevijver@plantentuinmeise.be text European Journal of Taxonomy 2020 2020-07-30 694 1 30 journal article 21375 10.5852/ejt.2020.694 521cb733-cb6c-4b74-8c94-957e2ad22336 3973347 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. Figs 132–138. Arcanodiscus saundersianus Goeyers & Van de Vijver sp. nov. SEM. Campbell Island holotype population, sample BAS272 (BR-4581). 132 . Frustule in girdle view with the narrow copulae. The arrows indicate the ligulae. 133 . Frustule in girdle view with the narrow copulae. The arrows indicate the fimbriate pars interior of the copulae. Note also the domed valve face. Parts of the upper layer are eroded showing small areolae. 134–135 . External valve face views showing the relatively small central area and the well-developed marginal ridges. 136 . External view of a valve in girdle view showing the low, almost flat valve face, the absence of marginal ridges and the broad mantle edge. 137 . Internal views of an entire valve showing several rimoportulae (arrows). 138 . Internal detail of the valve with an indicated rimoportula. Note also the rota on the areolae. Scale bars: 132–137 = 10 μm; 138 = 1 μm. 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 .