Navicula pseudocryptofallax, 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 : 211

Navicula pseudocryptofallax sp. nov.

Description: —LM ( Figs 21–36 ): Valves lanceolate with protracted rostrate to subcapitate ends, length 17.5–29.5 µm, width 5.0–6.0 µm. Axial area narrow, slightly widening towards valve centre; central area very small, irregular or indistinct. Striae strongly radiate, arched, becoming convergent towards the poles, 15.0– 16.5 in 10 µm, in valve centre long and short striae alternate. Areolae not discernible in LM. Raphe filiform, straight; terminal fissures indistinct; central pores straight, positioned close to each other.

SEM external valve surface ( Figs 37–39 ): Areolae apically elongate, areola openings at same level as valve surface. At valve apex two isolated areolae present with openings oriented approximately parallel to valve margin. Areola density 40–45 in 10 µm. Raphe sternum slightly elevated and widened at valve centre. Raphe branches straight. Central raphe endings clearly hooked to secondary valve side. Terminal fissures curved to secondary valve side.

SEM internal valve surface ( Fig. 40 ): Striae lie in shallow transapical depressions, striae wider than virgae. Areolae occluded by hymenes, two isolated areolae present at valve apex. Raphe opens obliquely to secondary valve side, raphe sternum slightly widened at centre. Accessory rib absent. Central raphe endings simple, straight, separated. Distal raphe terminates in well developed helictoglossae.

Type: — RUSSIA. Krasnodar Territory: vicinity of Afonka Khutor, small, intermittent pool in the riverbed of a tributary to the Adegoy River on its northern side, on filamentous algae and silt, 44.72635°N, 37.93951°E, 179 m asl, D.A. Chudaev, 29th May 2016 (Holotype: MW-D! slide # 509s1 = Fig. 22 ; isotype: slide LE A0000281 ) .

Etymology: —The specific epithet reflects the similarity with N. cryptofallax Lange-Bertalot & Hofmann in Lange-Bertalot (1993: 103).

Distribution and ecology: —The species is so far only known from the River Adegoy and its tributaries (samples 501, 502, 506, 507, 508, 509, 510). In the type material, where it occurs at a relative abundance of 7.5%, it is associated with the following Navicula taxa: N. adegoyensis sp. nov., N. antonii Lange-Bertalot in Rumrich et al. (2000: 155), N. avenacea , N. capitatoradiata , N. cryptotenella , N. gregaria , N. metareichardtiana , N. novaesiberica , N. oblonga ( Kützing 1833: 548) Kützing (1844: 97) , N. radiosa , N. tripunctata , N. trivialis Lange-Bertalot (1980: 31) (all occur at <1% abundance). The diatom assemblage at the type location is dominated by Encyonopsis spp. (48.6%) and Achnanthidium spp. (19.3%).

Figures

FIGURES 21–40. Navicula pseudocryptofallax sp. nov. 21–36. LM, type material, slide MW-D 509s1, Fig. 22 represents the holotype. 37–40. SEM, sample MW-D 502. Figs 37–39. External valve surface. Fig. 40. Internal valve surface. Scale bars = 10 µm (Figs 21–36), 2 µm (Figs 37–40).