Cocconeis cascadensis

Cocconeis cascadensis Stancheva, sp. nov. (Figs 1–33)

Description.Valves large, elliptical to slightly elongate-elliptical with rounded apices (Figs 1–12). SV striae parallel and straight at the centre, radiate and very slightly curved towards the apices; sternum narrow, linear (Figs 1,2, 5–7). Striae in the middle portion of the valve often separated by wider virgae on one side of the valve (Figs 1, 5,6, 10). Areolae coarse, transapically elongated, of different sizes and variable appearance, i.e., lineolate, rectangular, oblong or oval. The marginal areolae close to the mantle narrower and lineolate (Figs 5–7).

RV with straight, filiform raphe, narrow axial area and small elliptical central area (Figs 3, 4, 8, 11, 12). Striae parallel and straight at the centre, radiate and slightly curved towards the apices, with small and round areolae clearly distinguishable with LM, the central striae some-times slightly separated by wider virgae on one side of thevalve (Fig. 8). Striae interrupted near the valve margin by a thickened hyaline area with uneven margins and bumpy appearance (Figs 3, 4, 12).

In SEM, SV striae uniseriate. Areolae externally depressed, slit-like lumen enclosed in large crater-like structure (Figs 19, 20, 22); crater-like depressions variable in size, strongly developed in the central part of valve face (Figs 13–19), and weakly developed along the sternum and near the mantle (Figs 17, 18). Internally, areolae closed by hymenes with long, regular and oblique slits (Figs 21, 24). Several small pores visible between striae in many valves, both externally (Figs 13, 14, 17, 18, 20) and internally (Fig. 23). In SEM, RV striae uniseriate. Internally, areolae closed by hymenes with a marginal row of linear slits (Figs 32, 33). Striae interrupted by a slightly raised sub-marginal area separating a single row of marginal areolae (Figs 25–27). Submarginal area with irregular margins, internally bearing apically elongated bumps (Figs 28, 29). Raphe filiform, internally with proximal raphe fissures deflected on opposite sides and distal raphe endings with visible helictoglossae (Figs 25, 26). Externally, proximal raphe ends are drop-shaped, and distal ends are straight, distant from the margin. RV valvocopula margin with indentations (Fig. 30), open at one pole (Fig. 31).

Dimensions. Length: 15.7–40 μm; width: 8.7–22 μm;striae: SV: 7–12 in 10 μm, RV: 15–18.5 in 10 μm; areolae: SV: 3–7 per stria to a single areola near the apices, RV:18–24 in 10 μm.

Holotype. Slide GC 65323, The Academy of Natural Sciences Philadelphia Diatom Herbarium, USA. Holotype specimen is illustrated on Fig. 2. Isotype. Slide GC 65324 and cleaned material GCM5762, both from Montgomery Creek, The Academy of Natural Sciences Philadelphia Diatom Herbarium, USA.

Type locality. The new species was observed in a sample from Hat Creek (40.851099,−121.5364; 526PS1724) in Lassen National Forest in the Southern Cascade Mountain Range, California collected on 27 June 2016 by Jennifer York .

• Author
  Stancheva 2018
• Length Range
  15.7-40 µm
• Width
  8.7-22 µm
• Striae in 10µm
  7-12