Proschkinia vergostriata

Proschkinia vergostriata Frankovich, Ashworth & M.J.Sullivan, sp. nov. (Figs 66–78)

Light microscopy (Figs 66–69): Frustules in girdle view small, weakly silicified, rectangular with rounded ends and numerous copulae (Figs 66, 67). Frustule width 3.5–7.5 μm (n = 30). Valves narrowly lanceolate with weakly protracted, cuneate subrostrate apices (Figs 68, 69). Valve dimensions (n =30, natural and cultured populations): length 5.0–15.0 μm, width 1.5–3.0 μm, length/width ratio 3.9–6.2. Axial area very narrow with a distinct raphe-sternum (Fig. 68, arrow). Fistula evident in the central area (Fig. 69, arrow). Striae discernible near the central area, gradually becoming undiscernible towards apices, slightly convergent (Figs 66–69).

Scanning electron microscopy (Figs 70–78): External view: Valve face flat. Longitudinal silica strips absent. Striae uniseriate, their density often increasing towards the apices by up to 40%, 27 (central area)–43 (apex) in 10 μm. Striae composed of large rectangular areolae, decreasing in size towards the axial area (Figs 70–73), ca. 60 in 10 μm. Areolae adjacent to the raphe distinctly larger, clearly sunken (Figs 70–73). Striae nearly parallel at the central area becoming rapidly curved and strongly convergent towards the apices (Figs 70–73), continuing onto the mantle (Figs 70, 71). Mantle shallow, lacking a clear valve face/mantle junction (Figs 70, 71). Raphe located between very narrow silica ridges, weakly raised in the valve middle (Figs 70–73). Central area rectangular, almost symmetrical, formed by 1–2 shortened striae on each side of the raphe-sternum (Figs 71–73). Central raphe endings closely spaced, spatulate, slightly bent towards the secondary side of the valve (Figs 72, 73). Linear silica flange present next to the central area on the primary side of valve forming a hood, obscuring the external fistula opening (Fig. 72, arrow). Terminal raphe fissures strongly hooked towards the secondary side, extending onto the valve mantle (Fig. 70). Single, transapically elongated areola at the end of the hooked raphe fissures (Fig. 70, arrow). Unornamented areas on each hemivalve adjacent to polar raphe endings extending onto mantle margins (Figs 70, 71). Single row of apically elongated pores at apices poleward of polar raphe endings and unornamented areas (Figs 70, 71, 73). Internal view: Areolae squarish to elliptical, gradually decreasing in size towards the raphe-sternum, except for the central longitudinal row adjacent to the axial area composed of much larger, rounded areolae, clearly raised on the raphe sternum (Figs 74–76, 78). Raphe slit visible only at the central endings and the apices, opening laterally within a thick axial rib (Figs 74–76, 78). Central raphe endings simple, bent towards the fistula (Figs 75, 76, 78). A small knob-like pointed structure protruding laterally from the central nodule, opposite to the fistula (Figs 75, 76, 78). Internal fistula opening visible as a lateral expansion of the central nodule, covered by a domed oval structure (Figs 75, 78) but missing in some specimens (Fig. 76). Simple helictoglossae present at the thickened apices (Figs 74, 75). Isolated areolae occluded by hymenes poleward of the helictoglossae (Fig. 74). Cingulum composed of multiple open copulae (up to 16 observed; Figs 71, 77). Unperforated pars exterior of copulae overlapping the perforated pars interior of adjacent copulae producing an external appearance of the cingulum as unperforated bands (Figs 71, 77). Separated copulae revealing single row of rectangular pores on the pars interior (Fig. 77), ca. 4 in 10 μm.

• Author
  Frankovich, Ashworth and M.J.Sullivan 2019
• Length Range
  5.0-15.0 µm
• Width
  1.5-3.0 µm
• Striae in 10µm
  27-43, increasing from mid-valve towards apices