Diploneis elliptica (Kutzing) Cleve, 1894

Jovanovska, Elena, Levkov, Zlatko & Edlund, Mark B., 2015, The genus Diploneis Ehrenberg ex Cleve (Bacillariophyta) from Lake Hövsgöl, Mongolia, Phytotaxa 217 (3), pp. 201-248 : 230-232

Diploneis elliptica cf. var. ladogensis Cleve ( Figs 166–169 )

Valves are linear-elliptic with weakly convex margins and round ends. The valve length is 24.5–29.0 μm and the breadth is 9.5–11.0 μm. The axial area is narrow, expanding into a small, round to slightly elongate central area. The central area is ca. 1.5 μm wide. The longitudinal canal is narrow, linear and slightly expanded in the middle, with a single row of areolae throughout the whole length. Raphe branches are straight and simple, positioned with an expanded depression. Striae are parallel in mid-valve, becoming slightly radiate towards the distal ends of the valve, 12(13) in 10 μm, with round to rectangular areolae that are secondarily aligned in wavy longitudinal rows, 12 in 10 μm.

Observations: — Cleve (1891) drew Diploneis elliptica var. ladogensis with an elliptical outline and moderately large and round central area. Later, Hustedt (1930, 1937) provided drawings of Diploneis elliptica var. ladogensis with a more or less rhombic outline and round central area. The population observed from Lake Hövsgöl is characterized with an elliptical to linear-elliptic outline and a small and round to slightly elongate central area. However, in this study additional differences can be observed between Cleve’s drawing and the population from Lake Hövsgöl: size range (length: 60.0 μm vs. 24.5–29.0 μm; breadth: 25.0 μm vs. 9.5–11.0 μm); stria density (9 in 10 μm vs. 12(13) in 10 μm); and areola density (10 in 10 μm vs. 12 in 10 μm). These differences might be as a result of the size dimensions given from a single valve ( Cleve 1891), and/or because of the small number of observed valves in this study. Further analyses could potentially provide a greater size range in Lake Hövsgöl, which might overlap the measurements given in the original description.

Diploneis elliptica var. ladogensis closely resembles Diploneis meyeri Skabichevskii (1936: 709 , pl. 1, fig. 56). Both species are similar in valve outline, but differ in the size range (length: 33.7–48.6 μm in D. meyeri vs. 60.0 μm in D. elliptica var. ladogensis ; breadth: 18.0–23.4 μm in D. meyeri vs. 25.0 μm in D. elliptica var. ladogensis ), and in the structure of the longitudinal canal (wide in D. meyeri vs. narrow in D. elliptica var. ladogensis ). Additionally, thick silica furrows are present on the valve face in D. meyeri , interrupting and crossing the striae, which are not present in D. elliptica var. ladogensis . A year later, Skvortzow (1937) described a different unrelated species under the same name D. meyeri (an illegitimate later homonym). Due to the broader size range and the width of the longitudinal canal and the absence of silica furrows on the valve face, the population from Lake Hövsgöl is better situated as D. elliptica var. ladogensis (see Krammer & Lange-Bertalot 1986, fig. 108: 5, p. 658); however, due to size differences with the type we retain the “cf.” designation in our identification.

Ecology and Distribution: —M247A; M276A; M289A: found on rocks and sediments in 5 to 40 m deep collections from central and northern Lake Hövsgöl .

Figures

FIGURES 166–183. LM valve views. Figs 166–169. Diploneis elliptica cf. var. ladogensis. Figs 170–172. Diploneis pseudovalis. Figs 173–178. Diploneis subovalis. Fig. 179. Diploneis mongolica. Figs 180–183. Diploneis spectabilis. Scale bar = 10 μm.