Kobayasiella pseudostauron Lange-Bertalot

Kobayasiella pseudostauron (Lange-Bertalot) Lange-Bertalot (Figs 3 K-T; 8 A-G)

Iconographia Diatomologica 6: 272-275 (Lange-Bertalot 1999). — Naviculadicta pseudostauron Lange-Bertalot in Lange-Bertalot & Metzeltin, Iconographia Diatomologica 2: 87-88 (Lange-Bertalot & Metzeltin 1996).

ECOLOGY AND DISTRIBUTION. — Kobayasiella pseudostauron was commonly observed but not abundant in Tursujuq National Park, where it was found in 26 lakes with a mean relative abundance of 0.5% and a maximum abundance of 2.9% in lakes T2-D and 18-W. No clear autecological patterns were distinguishable. This species was found in circumneutral waters, with a pH optimum of 6.56 (Appendix 3). The type locality for this species is Julma-Ölkyy (Finland), which shows similar water conditions to those of Tursujuq Park: oligotrophic and weakly alkaline. Kobayasiella pseudostauron has a circumpolar distribution.

The frustules are rectangular and narrow in girdle view. The valves exhibit a linear to linear-lanceolate shape with subrostrate to subcapitate to capitate protruding ends. Based on a sample size of 12, the valve dimensions range from a length of 19 to 22.5 µm and a width of 3.5 to 4.0 µm. The stria density is 38-40 in 10 µm. The external valve face is flat. The axial area is linear to lanceolate and narrow. The central area is a large rectangular to stauros-fascia, which may or may not have small marginal striae (Fig. 8A, C, D). The raphe is linear, with a kink-like irregularity halfway between the mid-valve and apex (Fig. 8A, B). Externally, the central raphe fissures are widely spaced and exhibit a linear expansion with indistinct rounded ends (Fig. 8C, D). The terminal raphe fissures are curved, deflected, not hooked, and located on the secondary side of the valve opening, with an external elliptic to funnel-like depression (Fig. 8E, F). Internally, the raphe is located on a thickened sternum and appears straight, without a kink-like irregularity (Fig. 8G). The proximal raphe fissures are T-shaped, and the terminal fissures end on small elevated helictoglossae, isolated from the apex mantle (Fig. 8G). The striae are strongly radiate at the mid-valve and become strongly convergent at the apices, with four to six rows of pores per stria. A thickened valve margin separates the striae on the valve face from the striae on the mantle. From the mid-valve to the Voigt fault, the striae became straight to flexed halfway between the axial area and valve margin. From the Voigt fault to the apex, the striae became flexed to straight. Distinct Voigt faults are present on both the primary and secondary sides of the valve, located at 2/3 of the distance between the mid-valve and apex (Fig. 8E, G). The striae on the mantle are reduced and continuous around the apices. The striae are covered with four to six rows of small multiseriate pores. Internally, the pores are positioned between thickened virgae ribs.

The specimens of Kobayasiella pseudostauron fromTursujuq National Park are at the bottom of the size range, with slightly smaller (19-22.5 vs 20-24 µm) and narrower (3.5-4.0 vs 4.0- 4.7 µm) valves compared to specimens from the type locality. Some of the LM images from the type description have visible striae (e.g. Lange-Bertalot & Metzeltin 1996: pl. 35, figs 11, 13) which may suggest that this taxon has a wider stria range than reported (37-39 in 10 µm). The SEM internal views of the central area and the capitate ends match our SEM images. Kobayasiella pseudostauron is similar to K. jaagii (F.Meister) Lange-Bertalot:two small Kobayasiella taxa with a large central area or fascia. Kobayasiella jaagii is a larger species (24-27 vs 19-24 µm) and broader (5 µm vs 3.5-4.5 µm) with a lower stria density. Furthermore, K. jaagii has rostrate apices while K. pseudostauron has subcapitate to capitate apices and a full stauros-like central fascia. Specimens identified as K. jaagii from western North America are larger than the original description and bluntly rostrate, compared to the attenuated rostrate apices of K. jaagii in the original drawing of Meister (Bahls 2013), which is in line with the broader concept of the species presented by Germain (1981) and Krammer & Lange-Bertalot (1986).