Tursiocola bondei

DESCRIPTION–LM morphology: Cells motile and apochlorotic with few to numerous highly refractive putative oil droplets (Figs 4–9, 14). Frustules rectangular in girdle view with bluntly rounded ends (Figs 4–5, 8, 19–23) and porose copulae (Figs 19–23). Copulae pores located just below valve margins with relatively broad hyaline area in middle of cingulum (Figs 19–23). Valves isopolar and narrowly lanceolate to nearly linear with obtusely rounded apices (Figs 6–7, 9, 24–31). Valve measurements: length 15–34 µm, width 2.6–3.9 µm, length to width ratio 5–10, n ≥ 30. Raphe straight (Figs 24–31). Central raphe ends straight, appearing slightly expanded, terminating just within large, circular to diamond-shaped central area (Figs 24–31). Central area intersected by very narrow, linear fascia, extending to valve margin (Figs 19–24, 26, 28, 30). Transapical striae slightly convergent in middle of valve, becoming parallel towards apices, 22–26 in 10 µm, n = 39 (Figs 24, 26, 28, 30). Pseudosepta evident in girdle view (Figs 19–23). Each pseudoseptum extending over approx. 1/5 of the valve length from each apex, then continuing as narrow strips along the valve margin before connecting with the butterfly structure (Figs 25, 27, 29, 31).

DESCRIPTION–SEM morphology: External valve face with uniseriate transapical striae composed of irregular to transapically elongated areolae that are constricted along their length appearing similar in outline to overlapping pin holes (Figs 32–38), areola density approx. 25 in 10 µm. Relatively deep and steeply sloped mantle without clear transition between valve face and mantle (Figs 32–38). Mantle margin hyaline and heavily silicified (Figs 32, 34, 37, 38). Mantle margin at apices expanded into spur-like features extending towards valve face and overhanging apices (see arrow Fig. 35). These spur-like features asymmetric along apical axis and located to the secondary side of the valve, extending into groove created by the deflected polar raphe fissure (Figs 34–35, 38). Extension of mantle margin at apices resembles a corner of a picture frame, or a gable, or cornice, or eaves around a house when observed in valve view. We introduce the term “fastigium” (plural – fastigii), the Latin word for gable, to refer to this structure. Raphe within narrow axial area (Figs 33, 35–36). Central area connecting with hyaline area along valve margin (Figs 32, 37). Central raphe ends open into spathulate grooves (Figs 33, 36). Polar raphe ends deflected towards secondary side of valve then apparently bifurcating around fastigium (Fig. 35). Internally, pseudosepta extend from apices as siliceous plates concealing the internal apices and polar raphe ends (Figs 39–45), then continuing as narrow strips that run along valve margin (Figs 39–42) before widening into broad concave wings of butterfly structure that connects with circular central area (Figs 39, 41–42, 44). In some specimens, narrow areas of pseudosepta briefly widen towards their middle, forming oblong-shaped voids constricted in middle (Figs 39–40). Internally, raphe fissure slightly expanded in central area lying along center of thick siliceous rib (Figs 39–42, 44). Two rounded knob-like structures present on rib on opposing sides of raphe at valve center (Figs 39, 41–42, 44). Epicingulum composed of open valvocopula and up to three additional abvalvar open copulae (Figs 34, 37–38). Valvocopula wide in girdle view (Figs 34, 37, 38), flanged inward on pars interior at apices (Figs 41, 43, 46), and widening into pair of opposing tabs located at valve middle underneath butterfly structure (Fig. 38). A small round opening is often formed where the open ends of the valvocopula meet (Figs 44–45). Valvocopula has one complete advalvar row and one partial abvalvar row of scattered pores, 24–26 in 10 µm, located adjacent to valve margins (Figs 32, 34, 37–38, 46). Abvalvar copulae wide at apices quickly narrowing to very thin strips (Figs 34, 37) with single row of very small pores, 45–60 in 10 µm (Fig. 34).

• Author
  Frankovich, Ashworth and M.J.Sullivan 2018
• Length Range
  15-34 µm
• Width
  2.6-3.9 µm
• Striae in 10µm
  22-26