Cymbella alexandrovichii Glushchenko, Mironov & Kulikovskiy, 2023

Glushchenko, Anton, Mironov, Andrei, Kuznetsova, Irina & Kulikovskiy, Maxim, 2023, Cymbella alexandrovichii sp. nov. (Cymbellaceae, Bacillariophyceae), a new cymbelloid diatom species with predominantly biseriate striae from South-East Asia, Phytotaxa 630 (2), pp. 112-122 : 113-117

Cymbella alexandrovichii Glushchenko, Mironov & Kulikovskiy sp. nov. Figs 1–20 ; Fig. 2 represents the holotype.

LM description ( Figs 1–8 ):— Valves dorsiventral, asymmetrically lanceolate. Dorsal margin convex, ventral margin less convex. Some large specimens have a swelling in the central part. Ends not protracted, cuneate to bluntly rounded, sometimes subrostrate. Length 62.4–76.0 µm, breadth 14.9–16.5 µm. Maximal length/breadth ratio = 4.9. Axial area narrow, linear. Central area absent. Raphe filiform, reverse-lateral (see Krammer 2002, p. 324, pl. 67, fig. 3e), central raphe ends weakly deflected ventrally, tipped with inflated drop-shaped pores. Distal raphe ends are deflected to the dorsal margin. Stigmata 2–3, located on the ventral margin, sometimes not clearly separated from areolae. Striae almost parallel at the central part of valve, becoming radiate and condensing at the very valve ends, 7–8 in 10 µm in the central portion, 8–9 in 10 µm near the ends. Biseriate organization of striae is difficult to resolve in LM.

SEM, external valve surface ( Figs 9–14 ):— The valve face is flat ( Fig. 9 ). The central branches of the raphe are slightly widened ( Figs 9–10 , white arrowheads). Terminal raphe fissures do not reach the apical pore fields, strongly deflected to the dorsal margins ( Figs 9, 13–14 , black arrowheads). Apical pore fields located on the valve margins, consist of round pores, similar in shape and size to the adjacent areolae ( Figs 13–14 , white arrows). Stigmata are present ventrally, rounded and crater-like ( Figs 10–11 , black arrows). Each of the striae consists of two rows of areolae, arranged alternately, the areola closest to the axial area is single ( Fig. 12 , white arrowheads). In the central part of the valve, several dorsal biseriate striae may become uniseriate ( Fig. 11 , white arrowheads). Voigt discontinuities are present ( Fig. 9 , black arrow). Areolae openings in central part of the valve usually rounded ( Fig. 10 , black arrowheads). Areolae on the valve margins become uniseriate and slit-like ( Fig. 12 , white arrows), except for the striae at the valve ends, where they are rounded and biseriate ( Figs 13–14 , black arrows). Areolae (in one of the rows of one striae), 27–32 in 10 µm.

SEM, internal view ( Figs 15–20 ):— The raphe is arcuate ( Fig. 15 ). Central raphe endings are covered by the outgrowth of silica ( Figs 16–17 , black arrows). Distal raphe ends terminate with small helictoglossae ( Figs 19–20 , black arrowheads). Helictoglossae deviated to the dorsal margin of the valve and adjacent next to the last dorsal striae ( Figs 19–20 , black arrowheads). Alveolate striae are located in depressions between interstriae (virgae), occlusions absent ( Fig. 18 , black arrows). Voigt discontinuities are present ( Fig. 18 , white arrow). Interstriae wider than striae in the central part of the valves ( Figs 15–16 , white arrows), becoming noticeably narrower than striae near the valve ends ( Fig. 19 , white arrows). The stigmata openings rounded or elongated, surrounded by fine ingrowths from their perimeter ( Figs 16–17 , white arrowheads). The openings of the apical pore fields are closed ( Figs 19–20 , black arrows).

Type:— Laos, Vientiane Province, Nam Hinboun River (17°53.783’N, 104°45.667’E), leg. E.L. Konstantinov, coll. date 02.11.2011. Slide no. 01612 , holotype specimen illustrated in Fig. 2 (in collection of Maxim Kulikovskiy at the Herbarium of the Institute of Plant Physiology Russian Academy of Sciences, Moscow, Russia) .

Isotype: Slide no. 01612а , deposited in herbarium of Faculty of Forestry National University of Laos, Vietntiane ( NUOL) .

Etymology:— The specific name is given in honor of chamber singer Mikhail Davidovich Alexandrovich (1914– 2002).

Distribution: — As yet known only from the type locality.

Ecology:— Cymbella alexandrovichii sp. nov. was found in a periphyton from river of slightly alkaline pH (7.7), temperature—20 °C and low electrical conductivity (111 μS/cm).

Figures

FIGURES 1–8. Cymbella alexandrovichii sp. nov. LM, DIC, type material, slide no. 01612. Fig. 2 represents the holotype. 1–6. Size diminution series. 7. Details of the central area. 8. Details of the valve end. Scale bars = 10 μm (Figs 1–6), 2 μm (Figs 7–8).

FIGURES 9–14. Cymbella alexandrovichii sp. nov. SEM, type material, sample no. 01612. External valve surface. 9. The whole valve, note the slightly widened central branches of the raphe (white arrowheads); terminal raphe fissure (black arrowhead); Voigt discontinuities (black arrow). 10–12. Details of the central area, note the slightly widened central branches of the raphe (10, white arrowheads); biseriate (10, black arrowheads) and uniseriate striae (11, white arrowheads) with single slit-like (12, white arrows) or round (11–12, white arrowheads) areolae; ventral stigmata (10–11, black arrows). 13–14. Details of the apices, note the terminal raphe fissure (13, black arrowhead); biseriate striae on the valve mantle (13–14, black arrows); apical pore field (13–14, white arrowhead). Scale bars = 10 µm (Fig. 9), 2 µm (Figs 10, 12), 1 µm (Figs 11, 13–14).

FIGURES 15–20. Cymbella alexandrovichii sp. nov. SEM, type material, sample no. 01612. Internal valve surface. 15. The whole valve, note that the interstriae wider than striae (white arrows). 16–17. Details of the central areae, note the closed terminal nodule (16–17, black arrows); interstriae wider than striae (16, white arrows); rounded or elongated stigmata openings, surrounded by fine ingrowths from their perimeter (16–17, white arrowheads). 18. Internal structure of striae, note the Voigt discontinuity (18, white arrow). Alveolate striae are located in depressions between interstriae (virgae) (18, black arrows) and occlusions are absent. 19–20. Details of the apices, note the APFs (19–20, black arrows); helictoglossa (19–20, black arrowheads); the interstriae that are narrower than striae (19–20, white arrows). Scale bars = 5 µm (Fig. 15), 2 µm (Fig. 16), 1 µm (Figs 17–20).