Navicula adegoyensis, Chudaev & Jüttner & Levkov, 2021

Chudaev, Dmitry, Jüttner, Ingrid & Levkov, Zlatko, 2021, The genus Navicula (Bacillariophyceae, Naviculaceae) from the valley of the Adegoy River (Krasnodar Territory, Russia) and description of two new species, Phytotaxa 494 (2), pp. 208-218 : 210

Navicula adegoyensis sp. nov.

Description:—LM ( Figs 4–18 ): Valves lanceolate with very slightly protracted to subrostrate ends, length 16.5–20.5 µm, width 4.5–5.0 µm. Axial area very narrow, a distinct small rounded central area occupies about 1/3 of the valve width and is bordered by 4–5 regularly shortened striae. Striae slightly radiate and arched in valve centre, becoming parallel or very weakly convergent towards the ends, 18.5–21.5 in 10 µm. Areolae not discernible in LM. Raphe filiform, straight; terminal fissures indistinct, central pores straight, drop-like.

SEM external valve surface ( Fig. 19 ): Areolae apically elongate, areola openings at same level as valve surface. At valve apex few barely visible isolated areolae present; subapical striae contain inverted V-shaped areolae. Areolae density 45–48 in 10 µm. Raphe sternum slightly elevated at valve centre. Raphe branches straight. Central raphe endings straight, small, drop-like. Terminal fissures curved to secondary valve side.

SEM internal valve surface ( Fig. 20 ): Virgae of same width as striae, becoming narrower at valve ends. Internal areola openings located in shallow troughs. Areolae occluded by hymenes, 2–3 isolated areolae present at valve apex. Raphe opens obliquely to secondary valve side, raphe sternum hardly widened at centre. Accessory rib presents, separated from raphe sternum by shallow furrow. Central raphe endings simple, very slightly deflected to secondary side. Distal raphe endings well developed straight helictoglossae.

Type: — RUSSIA. Krasnodar Territory: vicinity of Afonka Khutor, Adegoy River , on silt, 44.72610°N, 37.93930°E, 190 m asl, D. A . Chudaev , 27th May 2016 (Holotype: MW-D! slide # 502s1 = Fig. 5 ; isotype: slide LE A0000280 ) .

Etymology:— The specific epithet has been chosen after the type locality, the River Adegoy, where the species was found.

Distribution and ecology: —The species is so far only known from the River Adegoy and one of its tributaries (samples 502, 506, 507, 508, 509, 510). In the type material, where it occurs at a relative abundance of 0.5%, it is associated with the following Navicula taxa: N. cryptotenella Lange-Bertalot in Krammer & Lange-Bertalot (1985: 62) (4.9%), N. pseudocryptofallax sp. nov. (1.9%), N. metareichardtiana Lange-Bertalot & Kusber in Kusber & Lange- Bertalot (2019: 1), N. gregaria Donkin (1861: 10) , N. avenacea ( Rabenhorst 1864: 214) Brébisson ex Grunow in Schneider (1878: 112), N. radiosa Kützing (1844: 91) , N. novaesiberica Lange-Bertalot (1993: 126) , N. tripunctata (O.F. Müller 1786: 52) Bory (1822: 128) , N. capitatoradiata Germain ex Gasse (1986: 86) (all occur at <1% abundance). The diatom assemblage at the type location is dominated by Achnanthidium spp. (26.8%), Diatoma spp. (15.8%), Nitzschia spp. (14.4%) and Encyonopsis spp. (9.6%).

Figures

FIGURES 4–20. Navicula adegoyensis sp. nov. 4–18. LM, type material, slide MW-D 502s1, Fig. 5 represent the holotype. 19–20. SEM, type material, sample MW-D 502. Fig. 19. External valve surface. Fig. 20. Internal valve surface. Scale bars = 10 µm (Figs 4–18), 2 µm (Figs 19–20).