Orthoseira groenlandica Goeyers, Kochman-Kędziora & Van de Vijver, sp. nov. (Figs 1–30)

Type:— GREENLAND, Qeqertarsuaq, sample DM27 (coll. date 27.VII.2002, 69°15’23.3”N / 53°30’26.5”W, leg. P. Ledeganck), holo-BR-4801! (Meise Botanic Garden, Belgium), iso- slide 428! (University of Antwerp, Belgium). The holotype is represented by Fig. 8.

PhycoBank registration:—http://phycobank.org/103791

LM (Figs 1–22): Frustules cylindrical in girdle view, solitary or occasionally in pairs, with their valve faces connected (Figs 1–6, frustules in pairs not shown). Longer filaments of more than two connected frustules up to now not observed. Cells 15–25 μm, mantle height ca. 8 μm. Valves disc-shaped (Figs 7–22). Valve diameter (n=30): 10–35 μm. Valve surface flat, sloping abruptly at the valve face/mantle junction, visible in LM as a darker circular edge. Central area small, max. 1/5 of the total valve diameter, irregular in shape, hyaline, with often scattered areolae present between the carinoportulae. 2–3 (occasionally 4) large, rounded carinoportulae present. No relationship noted between number of carinoportulae and valve diameter. Striae on the mantle uniseriate, composed of densely packed irregular series of areolae, up to 25 in 10 μm. Valve face areolae large, arranged in radiate, uniseriate striae of variable length, 14–18 in 10 µm. Large, scattered marginal spines distinctly present at the valve face/mantle junction. No caverns, internal undulations or internal valves observed. Copulae number variable. (Figs 1–6).

SEM (Figs 23–35): Cingulum composed of several broad, open copulae entirely covered with small siliceous papillae (Figs 23, 24) and bearing several irregularly arranged, often incomplete rows of small poroids (Figs 23, 24). Mantle shallow, often with a clear step halfway the valve mantle (Figs 25, arrow, 26) giving the abvalvar mantle edge a thickened appearance compared to the advalvar edge. Marginal pore fields absent. Mantle covered by an irregular pattern of flattened but thickened ridges, giving the entire mantle a dirty outlook. Ridges extending from the valve face onto the advalvar edge of the mantle, continuing into a scattered pattern of small siliceous plates (Figs 26, 26). Areolae visible between the small siliceous plates (Fig. 26). Valve face/mantle junction abruptly sloping with rounded edge (Figs 25, 26). Short, radiating ridges surrounding the entire valve margin (Figs 25–29). Short, robust, marginal spines irregularly scattered on the valve margin (Figs 25–32). Valve face flat (Figs 27–29), covered in the center by a dense pattern of irregular small and large siliceous plates, obscuring the carinoportulae (Figs 27–30). Radiating striae extending from the central area to the valve margin, composed of distinct, rimmed, rounded areolae. In oblique view, the marginal zone of the valve face presenting a dense, irregular pattern of shorter and longer, small spines and papillae between and around the areolae (Figs 30, 32). Internally, valve face flat, smooth (Fig. 33). Areolae appearing as small, rounded poroids (Figs 34, 35). Striae often interrupted by short, slit-like openings (Fig. 34, arrows). Carinoportulae unoccluded (Fig. 33), pit-like, ornamented with a rough pattern (Figs 34, 35). Several slit-like openings present between the carinoportulae (Figs 34, 35). Internal caverns not observed (Fig. 33).

Ecology and associated diatom flora:—The sample was collected from wet (unidentified) terrestrial bryophytes, covered by cyanobacteria such as Phormidium sp., in a splash zone under an overhanging cliff from where water was continuously dripping on the soil and mosses. Water squeezed out of the mosses had a pH of 9 and a conductivity of 76 µS/cm and contained almost no nutrients (Van de Vijver, unpubl. res.). The diatom flora was entirely dominated by only a handful of species with Luticola arctica Levkov & Metzeltin (in Levkov et al. 2013: 67) and Humidophila perpusilla (Grunow 1860: 552) R.L. Lowe (2014: 358) as the most dominant species, and Stauroneis obtusa Lagerstedt (1873: 36) and Orthoseira groenlandica being frequent but not dominant, pointing to the aerophilic character of the environment.