Navicula gogorevii Chudaev, Glushchenko, Kulikovskiy & Kociolek, 2020

Kulikovskiy, Maxim, Chudaev, Dmitry, Glushchenko, Anton, Kuznetsova, Irina, Krivova, Zinaida & Kociolek, John Patrick, 2020, Navicula gogorevii-a new, large-celled diatom species from Vietnam (Southeast Asia), Phytotaxa 428 (1), pp. 60-66 : 61

Navicula gogorevii Chudaev, Glushchenko, Kulikovskiy & Kociolek , sp. nov. ( Figs 1–26 )

Description.

LM ( Figs 1–14 ). Valves lanceolate with widely rounded apices, length 67.6–97.5 μm, width 11.4–13.1 μm. Axial area moderately narrow, linear, slightly widening towards the centre. Central area transversely expanded, variable in shape, occupying 1/2–4/5 of valve width, often with irregular border due to unequal shortening of central striae. Striae radiate at the valve centre, becoming convergent towards valve ends, 16.0–18.6/10 μm. Areolae well distinguishable in LM, 21.2–23.6/10 μm. Raphe slightly lateral, terminal fissures curved to the secondary valve side, central pores enlarged, straight or rare slightly deflected to the primary side. Central nodule asymmetrically expanded to the primary valve side.

SEM, external views ( Figs 15–20 ). Areolae open into distinct longitudinal grooves, separated by longitudinal siliceous strips, curved around central area and straight on the rest of the valve ( Figs 19 , black arrow). The margins of the grooves do not close up, so separate areolae are visible through the slits ( Fig. 20 , black arrow). Proximal grooves are interrupted by the central area. Grooves’ endings at central area and valve apices are pointed ( Figs 17, 20 , white arrowheads). Raphe-sternum is at the same level as the valve surface. Raphe slit is slightly lateral. Central pores enlarged (sometimes slightly asymmetrically), drop-shaped, undeflected or slightly deflected to the valve primary side ( Figs 17, 18 , white arrows). Terminal fissures sickle-shaped, lying mostly on the valve face ( Figs 19, 20 , white arrows). Pinhole-like openings of apical areolae are arranged in one row at the primary side of valve apex ( Figs 19, 20 , black arrowheads).

SEM, internal views ( Figs 21–26 ). Virgae and vimines lie on the same level, so transapical depressions (alveolae) are not formed. Areola openings are roundish-square to round. Internal width of areolae is larger than the external, so external slit-like openings are visible at the bottom of the areolae ( Figs 25, 26 ). Hymenes were not preserved during the material treatment. Raphe slits open obliquely to the secondary valve side and are visible only at the valve centre and apices ( Figs 23, 24, 26 , white arrows). Proximal raphe endings straight, positioned on the slight widening of rapheridge, with a short intermissio ( Figs 23, 24 , white arrows). Distal raphe endings are well-developed and terminate as straight or slightly deflected helictoglossae ( Figs 25, 26 , black arrows). Accessory rib prominent, unilaterally widened to the primary valve side ( Figs 23, 24 , black arrows), separated from raphe ridge by shallow longitudinal furrow ( Figs 23, 24 , black arrowheads). The widening of accessory rib (central nodule) gradually turns into the central area ( Figs 23, 24 , white arrowheads). Raphe-sternum widens at the apices forming well-developed terminal areas with cushion-like thickenings at the ends of accessory rib ( Figs 25, 26 white arrowheads). Internal openings of apical areolae are apically elongated and larger than the external ones ( Figs 25, 26 , black arrowheads).

Type: — VIETNAM. Ba Bể Lake, Bắc Kạn Province, benthos, N22°23.605´E105°36.856´, was collected by E.S. Gusev & M.S. Kulikovskiy, 29.04.2015 (in collection of Maxim Kulikovskiy at the Herbarium of the Institute of Plant Physiology Russian Academy of Science, Moscow, Russia), holotype here designated, slide no. 02168 = Fig. 3 ).

Etymology: —Species epithet honors the well-known Russian diatomologist Dr. Rinat Gogorev, Komarov Botanical Institute, Saint-Petersburg.

Distribution. As yet known only from the type locality.

Figures

FIGURES 1–14: Navicula gogorevii Chudaev, Glushchenko, Kulikovskiy & Kociolek, sp. nov. LM, DIC. Slide no 02168. Size diminution series. Figure 3 is of the holotype. Scale bar = 10 μm.

FIGURES 15–20: Navicula gogorevii Chudaev, Glushchenko, Kulikovskiy & Kociolek, sp. nov. SEM. External view. Figs 15, 16: Whole valve. Figs 17, 18: Central area. White arrows show the asymmetrical central pores. Fig. 17. White arrowhead shows the pointed groove ending. Figs 19, 20: Valve ends. Fig. 19. Black arrows show the distinct longitudinal grooves, separated by longitudinal siliceous strips, curved around central area and straight on the rest of the valve. White arrow shows the sickle-shaped terminal fissure, lying mostly on the valve face. Black arrowheads show the pinhole-like openings of apical areolae. Fig. 20. Black arrow shows the separate areolae, located in slit. White arrow shows the sickle-shaped terminal fissure, lying mostly on the valve face. Black arrowhead shows the pinhole-like openings of apical areolae. White arrowhead shows the pointed groove ending. Scale bars = 10 μm (Figs 15, 16); 2 μm (Figs 17, 18); 1 μm (Figs 19, 20).

FIGURES 21–26: Navicula gogorevii Chudaev, Glushchenko, Kulikovskiy & Kociolek, sp. nov. SEM. Internal view. Figs 21, 22: Whole valve. Figs 23, 24: Central area. White arrows show the raphe slits open obliquely to the secondary valve side. Proximal raphe endings straight, positioned on the slight widening of raphe-ridge, with short intermissio. Black arrows show the prominent accessory rib, unilaterally widened to the primary valve side. Black arrowhead shows the shallow longitudinal furrow. White arrowhead shows the extended accessory rib. Figs 25, 26: Valve ends. Black arrows show the helictoglossae. White arrow shows the raphe slit open obliquely to the secondary valve side. White arrowheads show the cushion-like thickenings at the ends of accessory rib. Black arrowheads show the apically-elongated openings of apical areolae. Scale bars = 10 μm (Figs 21, 22); 2 μm (Figs 23, 24); 1 μm (Figs 25, 26).