Cyclotella idahica Khursevich & Kociolek, 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 : 83-84

Cyclotella idahica Khursevich & Kociolek , sp. nov. ( Figures 1–9 )

Type:— USA. Oregon: Christmas Valley , Fort Rock, 44° 10' N, 121° 48' W, OD Section 7.9 m (see Colbath & Steele 1982), diatomite, collected summer 1981 (Circled specimen ( Fig. 2 ) on Slide 019002, material Kociolek Collection 0502 ( COLO!), holotype, designated here; duplicate slide of COLO 019002 deposited in Khursevich Collection, Minsk, Belarus, isotype, designated here) .

Additional material examined: — Idaho, Payette County, north bank of Willow Creek , 20 km NE on Willow Road from its intersection with Idaho highway 52, near center sec. 4, T. 8N., R. 2W., coll. S. Van Landingham. Diatomite is from Poison Creek Formation in the lower portion of Idaho Group, age approximately 11 to 12 mya.

Description:—Valve outline oval-elliptical, sometimes nearly circular, with several girdle bands. Dimensions of the major axis 8.0–48.0 µm, minor axis 6.5–46.0 µm. Valve surface is divided into two distinct zones. Central zone oval to elongate, transversely undulate, with irregularly arranged areolae, becoming more or less radiate, 7–10/ 10 µm in large specimens only. Areolae with internal domed velum and external foramina. Fultoportulae on the valve face have two to four satellite pores, but those with three satellite pores are located mainly in the concave part of the valve face internally. Fultoportulae with small aperatures externally. External valve face is often covered with bumps. Marginal zone extends from 1/3 to 1/2 of the valve radius, and consists of alveolate striae in fascicles, 7–10/ 10 µm, separated by hyaline interfascicles. Each fascicle consists of 3–4 parallel or slightly wavy rows of small puncta. Puncta number 40–60 in 10 µm measured radially, in small specimens. In large specimens, 5–6 puncta at the margin become bi- or triseriate on the valve face. Striae fascicles are all of the same length. A ring of marginal chambers can be observed internally. Adjacent chambers are divided by thicker costae. Each chamber encompasses mostly 2 or 3 alveolar openings separated by thinner costae bearing marginal fultoportulae with 3 satellite pores, 4–6/ 10 µm. Externally marginal fultoportulae are represented by short tubes, which are often broken. A single rimoportula with a slit oriented radially or subradially occurs in association with a thinner costa. The rimoportula has a small external opening. Spines are irregular in number, being located on the interfascicles at the margin. Granules occur along the mantle edge.

Cyclotella idahica differs from C. jonesii McLaughlin (1992: 96 , figs 1–11; see Figs 70–77 herein) by the smaller size of the valves, circular or oval valve shape, consistently having valve face fultoportulae, and having more pronounced bumps and granules on the valve face. Despite these differences, the two species share many features and appear to have close phylogenetic affinities.

Figures

FIGURES 1–5: Cyclotella idahica. LM. Valve views showing highly undulate valve face. Fig. 2. Holotype. Scale bar = 10 µm.

FIGURES 6–9: Cyclotella idahica. SEM. Figures 6, 7, 9. external views. Valve views showing transversely undulate central area with irregularly arranged areolae and covered by bumps. Present are external openings of areolae and short tubes of marginal fultoportulae. Spines and/or spines bases are found on the valve face/mantle junction. Scale bars = 1 µm. Figure 8, internal view. Valve view showing location of one fultoportula on the valve face. Arrow indicates position of the rimportula. Scale bar = 1 µm.

FIGURES 70–71: Cyclotella jonesii. LM. Figure 70 is of Morphotype 1. Figure 71 is of Morphotype 2. Scale bars = 10 µm.

FIGURES 72–77: Cyclotella jonesii. SEM. Figures 72, 73. External valve views of Morphotype 1. Fascicles are comprised of fine areolae, while the tangentially undulate center has larger areolae. Marginal fultoportulae have tubular external openings, located on or about every other costa. Scale bars = 10 µm, respectively. Figure 74. External valve view of Morphotype 2. Multiseriate fascicles are comprised of areolae much smaller than those in the center of the valve. Scale bar = 2 µm. Figure 75. Internal valve view of Morphotype 1. Thick and thin costa are present. Central areolae are numerous. Scale bar = 10 µm. Figures 76, 77. Internal valve view of Morphotype 2. Marginal fultoportulae are located on recessed costae, and have 3 satellite pores. Central fultoportula is present, situated among scattered areolae with domed cribra. Scale bars = 2, and 1 µm, respectively.