Gomphonema californicum

Gomphonema californicum Stancheva & Kociolek, sp. nov. (Figs 1–27)

LM observations

Valves are lanceolate-clavate with rounded head pole and narrower foot pole. Cells are 5.6–8.3 μm wide, 22–67 μm long (Figs 1–13); initial cell 10 μm wide, 71 μm long (Fig. 14). Striae are slightly radiate at the center of the valve 10–13 in 10 μm, becoming denser up to 15 in 10 μm near both apices and strongly radiate toward the foot pole. Striae composed of areolae, which are coarser and distinguishable near the head pole, 28–32 in 10 μm. Striae sometimes are interrupted, particularly around the central area (Figs 2 and 3). Axial area narrow, lanceolate. One, occasionally two median striae on both sides of the central area are shorter than the others (Figs 4–6). Central area is rectangular transversely extended, delimited by two or three curved striae (Figs 2, 6, 8, 10), rarely elliptical (Fig. 4). One isolated stigma is positioned close to the proximal raphe ends. Sometimes one or a few small indistinct depressions are present in the central area, not easily resolvable with LM (Fig. 2). The raphe is lateral, slightly undulate. Frustules are slightly cuneate in girdle view with single or double irregular rows of puncta on each mantle, in some specimens interrupted near the middle (Figs 12 and 13).

SEM observations Externally, striae are uniseriate, composed of slit-like (lineola-like) areolae, which extend onto the mantle (Fig. 15–18). Areolae near the head pole (Fig. 19) are coarser and longer than the areolae close to the foot pole (Fig. 20). Areolae adjacent to the axial area are shorter and slightly undulate or c-shaped (Figs 15, 16, 19). Small areolae with circular external openings form: (1) the tips of the median short striae and the adjacent two or three striae (Figs 22, 23), and (2) the entire basal stria at the foot pole (Figs. 17, 18, 20). Apical pore field with porelli, separated from striae by a hyaline area is present at the foot pole (Figs 15–18, 20). The porelli are either regularly ordered within the apical pore fields (Fig. 15) or split by a narrow, unornamented area (Fig. 20). Distal raphe ends are deflected before the apices and extend into the mantle (Figs 19, 20). A small single apical spine is present at the head pole (Fig. 19), better observed in girdle view (Figs 17, 18, 21). In some specimens the spine may be very small or missing (Fig. 16), but in other specimens is pronounced and visible with LM (Fig. 13) In the central area, one isolated stigma with a circular opening is positioned close to the dilated and drop-shaped proximal raphe ends (Figs 22, 23). Sometimes, one or two small indistinct depressions are visible near the stigma in the central area (Fig. 23). These do not extend through the valve and are not visible on the internal side of the valve. Each mantle with pores in an irregular single row, becoming double near the head pole, and more widely spaced near the middle (Figs 17, 18). Internally, the helictoglossa and pseudosepta are visible at both poles (Figs 24, 27). The central nodule is slightly raised, bearing a slit-like stigma opening and dilated and recurved proximal raphe ends (Figs 25, 26).

Type:—USA. California: Digger Creek, Sierra Nevada Mts, 40.44284º N, 121.72501º W, Nathan Mack, August 31, 2015 (holotype UC2050494 circled specimen on slide; isotype RS! 007, circled specimen on slide and material, CSUSM, USA).

Etymology:—The epithet refers to the USA state of California, where the species was first observed.

Distribution and ecological notes:—Found in four sites in the Sierra Nevada Mts, CA (elevation 1133 to 1902 m a.s.l.). Habitats are generally characterized by low nutrients (total nitrogen (TN) <0.1 mg L-1, total phosphorus (TP) <0.05 mg L-1), low conductivity (<107.6 μS cm-1), slightly alkaline (35–76 mg L-1 CaCO3), and pH 8.1–8.5 (see Table 1).

Comments: —In terms of outline, and overall dimensions, this species resembles G. dichotomum Kützing (1833: 569) as illustrated by Reichardt & Lange-Bertalot (1991) and G. grasmueckii Lange-Bertalot & Reichardt (Lange- Bertalot 1993). Striae densities of both diatoms, however, are lower compare to the California specimens having striae that are 10–13 in 10 μm, and rarely up to 15 in10 μm (Table 2). Furthermore, the shape of central area differs among three species, being significantly smaller in G. grasmueckii. Perhaps more importantly, ultrastructurally the three species are quite different. Reichardt & Lange-Bertalot (1991) show G. dichotomum to have large c-shaped areolae uniform throughout the entire valve , while in G. californicum the areolae are variable in shape. In G. grasmueckii areaolae are lineola-lake and circular, but the stiae are only partially uniseriate, becoming biseriate toward the mantle (Lange-Bertalot 1993). The presence of an apical spine at the head pole is an unique feature of G. californicum.

• Author
  Stancheva and Kociolek 2016
• Length Range
  22-67 µm
• Width
  5.6-8.3 µm
• Striae in 10µm
  10-15