Cymbopleura laszlorum Bahls & Luna, 2018

Bahls, Loren & Luna, Tara, 2018, Cymbopleura laszlorum spec. nov. (Cymbellaceae, Bacillariophyceae), a glacial relic from a calcium-rich floodplain fen in southwestern Montana, USA, Phytotaxa 349 (1), pp. 47-53 : 49-51

Cymbopleura laszlorum Bahls & Luna spec. nov. Figs 3–12 , 24–29

Valves are elliptic-lanceolate with convex margins and rostrate to subrostrate apices. Length 41–54 μm; width 9.7–11.4 μm. Valves are symmetric with respect to both the apical and transapical axes. The axial area is about three times the width of the raphe and widens gradually towards the central area. The central area is moderately large and variable in shape, most often transversely elliptic to rectangular, sometimes shaped like a bow tie. The raphe is lateral, narrowing towards the ends. Proximal raphe ends are deflected gently towards the ventral margin and tipped with slightly inflated pores. Terminal raphe fissures are hook-shaped and concave towards the dorsal margin. Striae are uniseriate and radiate throughout, 14 in 10 μm at the valve center, up to 22 in 10 μm at the apices. Areolae are also variable in density, 20 in 10 μm in striae at the valve center, up to 30 in 10 μm at the apices. [n = 26 specimens]

SEM:—In external valve view, areolae are simple and transapically oblong ( Figs 25, 26 ). Occlusions and secondary structures (e.g., vimines) are absent. Striae continue around the valve apices ( Fig. 26 ); apical pore fields are absent. Costae between striae are wide relative to the striae themselves. External raphe fissures are narrow, becoming much wider at the terminal fissures ( Fig. 26 ). Internally, areolae are arranged end-to-end in trough-like alveoli and separated by narrow intercostae ( Figs 28, 29 ). Internal raphe fissures are wide, narrowing towards the terminal and proximal ends. Raphe branches terminate in simple helictoglossae ( Figs 27, 29 ). Proximal raphe ends are hooked and separated by a wide intermissio ( Fig. 28 ). A flap of silica with a curved edge overlies the central nodule on one side and merges with it at its center ( Fig. 28 ).

Holotype:— USA, Montana: East Fork O’Dell Creek , fen pool no. 4, 1567 m a.s.l., 45.2743 °N, - 111.2750 °W, 24 July 2017, coll. Tara Luna, Slide No. 49-69, MONTU ! Holotype specimen is in Fig. 5 .

Isotype:—Slide No. 136-34, Montana Diatom Collection (MDC), Helena.

Paratype:— USA, Montana: East Fork O’Dell Creek, fen pool no. 2, 1567 m a.s.l., 45.2738 °N, - 111.7255 °W, 24 July 2017, coll. Tara Luna, Slide No. 49-67, MONTU!, Slide No. 136-32, Montana Diatom Collection (MDC), Helena.

Differential diagnosis:—The species most similar to C. laszlorum in North America is C. stauroneiformis (Lagerstedt) Krammer (2003: 86) , an Arctic species described from Spitsbergen ( Figs 13–19 ). The two species have very similar morphometric values and both have central areas in the shape of a fascia, however C. laszlorum has wider (10–12 μm vs. 8–11 μm) and more elliptic valves with wider apices ( Table 2). Other North American species of Cymbopleura , including C. geofriedana Reichardt (2004: 428) and C. tynnii (Krammer) Krammer (2003: 30) , have similar valve and end shapes as well as comparable striae and areolae densities ( Figs 20–23 , Table 2), however Cymbopleura geofriedana ( Fig. 20 ) is much smaller (17–30 μm long) than C. laszlorum (41–54 μm long) and C. tynnii ( Fig. 23 ) is much larger (48–94 μm long).

Two undescribed taxa from Kazakhstan and the Swiss Alps ( Figs 21, 22 ) have wider (13–15 μm), more elliptic valves than C. laszlorum , but otherwise similar shapes, central areas and stria densities ( Table 2). The taxon from Kazakhstan ( Fig. 21 ) appears to be conspecific with Cymbopleura mongolica Metzeltin et al. (2009: 30) , which has valves with comparable shape and morphometrics ( Table 2). The taxon that most closely resembles C. laszlorum lives at 4800 m a.s.l. in the Everest region of Nepal: Cymbopleura cf. mongolica ( Van de Vijver et al. 2011: 257) . This taxon differs from C. mongolica by its smaller dimensions (10–11 vs. 12– 14 μm wide) and slightly higher stria density (17–19 vs. 15–17 in 10 μm). It differs from C. laszlorum by the shape of the ends, which are subcapitate rather than rostrate, and by a higher areola density (30–35 vs. 20–30 in 10 μm) ( Table 2). All of the taxa discussed above are from boreal or alpine habitats in the northern hemisphere.

Diatom associates:—At the type locality, Cymbopleura laszlorum was an uncommon (<1 % abundance) but visually conspicuous element of a benthic diatom association dominated numerically by Mastogloia lacustris (Grunow) Grunow in Van Heurck (1880: 70), Cymbopleura florentina (Grunow) Krammer (2003: 99) , and Epithemia argus (Ehrenberg) Kützing (1844: 35) , in decreasing order of abundance.

Etymology:—The new species is dedicated to the Jeff Laszlo family for its steadfast stewardship of this rare and invaluable wetland resource.

Figures

FIGURES 3–23. Transapically symmetric species of Cymbopleura with central fasciae and closely-spaced striae. 3–12. Cymbopleura laszlorum spec. nov. 3–9. Specimens from the type locality. Holotype specimen is in Fig. 5. 10–12. Specimens from the paratype locality. 13–19. Cymbopleura stauroneiformis. 13–15, 18, 19. Various tundra locations along the Back, Coppermine and Hood River corridors, Nunavut, Canada. 16, 17. Wet grassy meadow near Granite Gorge, Clearwater River, northern Saskatchewan, Canada. 20. Cymbopleura geofriedana from September Mountains Lake, Coppermine River corridor, Nunavut, Canada. 21. Cymbopleura sp. “Kasachstan” (Krammer 2003: 87, pl. 98, fig. 24). Photo by H. Lange-Bertalot. 22. Cymbopleura sp. “Messikommer” (Krammer 2003: 87, pl. 98, fig. 23). 23. Cymbopleura tynnii from wet hummocks near the Baillie River, Nunavut, Canada. Scale bars = 10 μm.

FIGURES 24–29. SEM images of Cymbopleura laszlorum spec. nov. 24–26. External valve views. 27–29. Internal valve views. Scale bars: 24, 27 = 5 μm; 25, 26, 28, 29 = 1 μm.