Punctastriata davidwilliamsii Van de Vijver & C.E.Wetzel, sp. nov. (Figures 1–33, 100–107)

Description:––Frustules rectangular in girdle view (Figs 1, 2), solitary or in pairs. Valves heteropolar, lanceolate with convex margins throughout its entire cell division cycle (Figs 3–33). Head pole protracted, truncated-rostrate, usually clearly depressed, lacking an apical pore field (Figs 100–106). Foot pole in longer specimens distinctly elongated, narrowly rostrate, in shorter valves only shortly elongated. Distinct apical pore field present on foot pole, composed of at least 4 long rows of very small porelli (Figs 102, 107). Valve dimensions (n=40): length 8–17 μm, width 4–5 μm. Sternum narrow but distinct, zig-zag shape, as raised as the virgae (Figs 101–105). Striae almost parallel to very weakly radiate in smaller specimens, 10–12 in 10 µm, stretched ovate in shape, from mantle to sternum. Broadest part on the mantle, becoming gradually more acute towards the sternum. Striae composed of with 2–4, occasionally 5 rows of small, rounded areolae (Figs 101–105). Viminules present in entire stria (Figs 101–105). Abvalvar part of the mantle with a broad hyaline edge (Figs 101, 106). Small, elongated mantle plaques present at the mantle edge (Fig. 106). Spines flattened, concave on its back, usually originating from virgae at the valve face/mantle junction (Figs 101, 102, 104, 105), with elliptical base of about the same width of the vimines they sit on. Spine body solid, usually with a flared, skirt-like projection, sometimes surrounding the entire base of the spine (Figs 101, 106, white arrows). Occasionally, spines emerging from the vimines (Fig. 103) or even from both virgae and vimines (Fig. 107).

Type:— BELGIUM. Frahan, Semois river, Belgium, coll. date August 1879, leg. C.H. Delogne (holotype slide BR-4922 = Fig. 9, isotype slide 471, University of Antwerp, Belgium).

PhycoBank registration:—www.PhycoBank.org/106041

Etymology: —The species is named in honour of our well appreciated friend and colleague, Dr. David M. Williams (Natural History Museum, London, UK), in recognition of his incredible contributions to diatom taxonomy in general, and araphid taxonomy in more detail. Without his insights and efforts, the taxonomy of araphid diatoms would have been much more confusing.