Cyclotella discostelliformica Kociolek & Khursevich, 2013

Kociolek, J. P. & Khursevich, G. K., 2013, Morphology of some fossil lacustrine centric species from the western United States assigned to the genus Cyclotella (Bacillariophyta), including four described as new, Phytotaxa 127 (1), pp. 81-99 : 86-90

Cyclotella discostelliformica Kociolek & Khursevich , sp. nov. ( Figs 25 –39)

Type:— USA. Oregon: Klamath County, Sprague River, Drews Road, diatomite, (Circled specimen ( Fig. 31 ) on CAS Slide Number 1026029, material CAS Accession Number 701883 ( CAS !), holotype, designated here; duplicate of CAS Slide Number 1026029 deposited in Khursevich Collection, Minsk, Belarus, isotype, designated here).

Additional material examined: — USA. Oregon: Klamath County, NE Sprague River Bridge, CAS Accession Number 600180, Slide Number 433093 ( CAS !)

Description: —Valve outline nearly circular, with several girdle bands, 5.0–17.0 µm in diameter. Valve surface is divided into two distinct zones with different morphologies. The central area is distinctly concave or convex with irregularly arranged areolae (5 to 17) and one to three valve face fultoportulae. The latter have three satellite pores internally and open by small aperatures externally. This central zone is separated from the marginal zone by a wide hyaline ring. Small specimens have simple alveolae. Marginal fultoportulae are located in small fovae on the gentle slope of costae. A single rimoportula has internal elongated slit and is positioned within the alveolar opening close to one of the costae. The marginal zone extends from 1/3 to ½ of the valve radius and consists of alveolate and fasciculate striae, 8–10/ 10 µm, divided by hyaline interfascicles. Interfascicles become broader towards the margin. Each fascicle has one-two rows of smaller puncta, which have a row of larger puncta on each side. Striae fascicles are of equal length. A ring of marginal chambers, separated by thicker costae, is evident internally. Alveolar chambers appear simple and complex in larger specimens. Complex alveolae are comprised of alveolar openings divided by thinner costae. The thinner costae bear marginal fultoportulae. Each fultoportula has three satellite pores, and number 4 in 10 µm. Externally, marginal fultoportulae are represented by small, circular openings. A single rimoportula is located on a thinner costa or along the slope of one of the costae. External rimoportula opening is a small, but distinct, slit. Granules may occur along the edge of the mantle.

FIGURES: 38–39: Cyclotella discostelliformica . SEM. Figure 38. External view showing opening of rimoportula and fine nature of the areolae. Scale bar = 1 µm. Figure 39. Internal view showing large rimoprotula (arrow) located on the side of a costa. Central fultoportula with 3 satellite pores is evident. Scale bar = 1 µm.

Cyclotella discostelliformica differs from C. idahica by its smaller size, presence of strongly concave or convex central area, external expression of the rimoportula (a distinct slit in C. discostelliformica ; a small circular opening in C. idahica ) and the absence of spines.

This new species appears in the light microscope to resemble Discotella stelligera (Cleve & Grunow) Houk & Klee (2004: 209 , figs 23, 24) but differs in the position of the rimoportula and marginal fultoportulae, (between two costae in D. stelligera and on thinner costae in C. discostelliformica ). Moreover, marginal fultoportulae in C. discostelliformica have three satellite pores; D. stelligera has marginal fultoportulae with two satellite pores.

Figures

FIGURES 25–31: Cyclotella discostelliformica. LM. Valve views showing highly undulate valve face. Fig. 31. Holotype. Scale bar = 5 µm.