Cymbella fontinalis

Holotype: slide no. 50-21, University of Montana Herbarum (MONTU), Missoula. Fig. 33 is an image of the holotype specimen; sample no. 492301, Montana Diatom Collection, Helena (collected by L. Bahls on 24 October 2017).

Isotype: slide no. 136-87, Montana Diatom Collection, Helena.

Type locality: USA, Montana, Cascade County, Giant Springs near Great Falls.

Etymology: The attributive adjective fontinalis means "of or from the fountain" and refers to the seeps, springs and spring creeks where this taxon is most often found.

Description: Plastids are H-shaped with a central saddle-shaped pyrenoid lying on the dorsal side of the girdle (Figs 11-14). Vavles are dorsiventral with actutely rounded apices. Dorsal margin is moderately arched; ventral margin is slightly convex to nearly flat. Valve length = 38-98 µm; valve width = 11-16 µm. Axial area is very narrow, barely wider than the raphe. Central area is elliptic and small to moderately large. Raphe is distinctly lateral, becoming reverse-lateral at the proximal ends. Proximal raphe ends are deflected dorsally at a 45°angle. Dorsal striae are radiate throughout; ventral striae are parallel in the valve center and radiate towards the apices. Striae are uniseriate and number 8-10 in 10 µm in the valve center, 11-13 in 10 µm near the apices. Stigmata number 2-7 and are somewhat separated from the ends of the median ventral striae. Areolae number 18-28 in 10 µm.

SEM: External foramina of the areolae are slightly curved, apically elongate slits (Figs 42-44). Striae continue uninterrupted onto the valve mantle (Fig. 44). Proximal raphe ends are strongly looped towards the ventral margin (Fig. 43). Striae terminate at the distal raphe ends on the dorsal side of the valve; on the ventral side they transition to a well-developed apical pore field (Fig.42). Valve cingula are without ornamentation (Fig. 42). Internally, the intermssio (the gap between the proximal raphe ends) is obscured by a flap of silica, the edgy of which gives the appearance of a continuous raphe fissure across the central nodule (Figs 45-47). Internal areola openings are ellipsoid and separated by wide vimines (Figs 46,47). No hymenes or cribra were observed. The margins of the stigmata are lined with tooth-like projections (Fig. 46). The terminal raphe fissure bisects a lobed helictoglossa that is inclined dorsally at some distance from the valve apex (Fig. 47). Internally, each column of poroids in the apical pore field is partially covered by a knobby jointed ridge of silica (Fig. 48).

• Author
  Bahls 2018
• Length Range
  38-98 µm
• Width
  11-16 µm
• Striae in 10µm
  8-10 in valve center, 11-13 near apices