Navicula striolata

Wojtal, Agata Z., Ognjanova-Rumenova, Nadja, Buczkó, Krisztina, Siwek, Janusz & Vijver, Bart Van De, 2015, Revision of Navicula striolata (Grunow) Lange-Bertalot and N. rumaniensis Hustedt with the description of N. friedelhinziae sp. nov., Phytotaxa 204 (3), pp. 177-192 : 182

Navicula striolata (Grunow in Cleve & Grunow) Lange-Bert. in Krammer & Lange-Bertalot ( Figs. 22–28 )

Material examined:— POLAND: springs in Centuria, Imbramowice, Jangrot, Kroczyce, Ołudza, Siamoszyce, Sokolniki, Węgrzynów; leg. A.Z. Wojtal; collected in 2009–2013.

LM:— ( Figs. 22, 23 ): Valves narrowly lanceolate with clearly convex margins and broadly rounded, non-protracted apices. Valve dimensions (n=20): length 55–73 μm, width 11.0–12.5 μm. Axial area linear to linear-lanceolate, rather narrow. Central area usually small, apically elongated, bordered by alternating longer and shorter striae. Raphe branches distinctly lateral. Proximal raphe ends unilaterally deflected towards the secondary side of the valve, indicated by a clear Voigt discordance. Distal raphe endings apparently hooked to the opposite side as the proximal endings ( Fig. 22 ). Striae distinctly radiate and more widely spaced in the mid-valve becoming parallel or slightly convergent and more densely arranged towards apices, 8–9 in 10 μm. Lineolae clearly discernible in LM, 24–25 in 10 μm.

SEM:— ( Figs. 24 – 28 ): Raphe sternum prominent and elevated through most of the axial area bordered by a distinct, narrow groove, becoming confluent towards the apices ( Fig. 24 ). External proximal raphe ends undulating, slightly expanded to even spathulate, forked with a distinct silicate tongue, entering the raphe fissure ( Fig. 26 ). External distal raphe fissures extending slightly curved to one side and continuing onto the valve apex mantle. Transapical striae composed of rather elongated lineolae with foramina of comparable length as the virgae. Near the valve apex, striae replaced by large hyaline area.

Internally, raphe slit very narrow, straight, running on the side of a thickened, raised sternum ( Fig. 27 ). Proximally, simple raphe ends straight, located on a small, elevated ( Fig. 28 ) central nodule. A pronounced accessory rib running apically along the entire valve excluding the central nodule. Distal raphe endings terminating in small helictoglossae, surrounded by hyaline area. At the valve apex, one large pore visible. Striae located within elongated grooves, bordered by raised virgae.

Figures

FIGURES 22–28. Navicula striolata (Grunow in Cleve & Grunow) Lange-Bertalot. 24–28. SEM images showing typical characters of the species, i.e. raphe sternum prominent and elevated through most of the axial area; external proximal raphe ends forked with a distinct silicate tongue, entering the raphe fissure; raphe endings terminating on small helictoglossae; raphe ends are straight, located on a small, elevated central nodule. Modern samples collected from various localities in Poland. SEM: Ołudza locality. Scale bars: 24, 25 = 30 μm, 26–28 = 5 μm. LM: scale bar = 10 μm.