Kobayasiella subtilissima (Cleve) Lange-Bertalot

Alibert, Marie, Hamilton, Paul B., Pienitz, Reinhard & Antoniades, Dermot, 2023, Small naviculoid species of Kobayasiella Lange-Bertalot, Adlafia Moser, Lange-Bertalot & Metzeltin, Nupela Vyverman & Compère and Sellaphora Mereschowsky from Tursujuq National Park, Hudson Bay region, Nunavik, Québec, Cryptogamie, Algologie 20 (9), pp. 157-187 : 166

Kobayasiella subtilissima (Cleve) Lange-Bertalot

( Figs 2 AC-AO; 6 A-F)

Iconographia Diatomologica 6: 268 ( Lange-Bertalot 1999). — Navicula subtilissima Cleve , Actas Societas Pro Fauna et Flora Fennica 8 (2): 37 ( Cleve 1891).

ECOLOGY AND DISTRIBUTION. — Kobayasiella subtilissima was found in 29 lakes in this study. However, it was present in low relative abundances (mean 1.1%) with a maximum of 10.7% in Lake 18-R. This species was more common in acidic conditions ( Appendix 3 ) with a pH optimum of 6.2 and a relatively low DIC optimum of 0.76 mg /L ( Appendix 4 ). A globally distributed species under consistent environmental conditions.

DESCRIPTION

The frustules are rectangular and narrow in girdle view. The valves exhibit a linear-elliptic to linear-lanceolate shape with subcapitate to capitate ends. Based on a sample size of 22, the valve dimensions range from a length of 25 to 32.5 µm and a width of 5.5 to 6.5 µm. The length-to-width ratio is 4.3 to 5.0.The stria density ranges from 36 to 40 in 10 µm. The external valve face is slightly recessed around the central area. The axial area is linear to lanceolate and narrow. The central area is an expanded axial area, small and round to elliptic, with 6-7 marginal striae oriented between widely spaced proximal raphe fissures. The raphe is linear, with a sharp kink-like irregularity closer to the mid-valve than the apex ( Fig. 6A ). Externally, the central raphe fissures are linearly expanded with rounded ends. The terminal raphe fissures are bent and deflected on the valve face to one side, opening with an external linear to funnel-like groove ( Fig. 6E ). Internally, the raphe is located on a thickened sternum and appears straight, without a kink-like irregularity ( Fig. 6B ). The proximal raphe fissures are T-shaped and located on an elevated central nodule, while the terminal fissures end on elongated helictoglossae, isolated from the apex mantle ( Fig. 6D, F ). The striae are radiate at the mid-valve and become strongly convergent at the apices. From the mid-valve to the Voigt fault, the striae are flexed, and from the Voigt fault to the apex, the striae change from being flexed to straight. The mantle striae are interrupted by a hyaline ridge at the valve face/mantle junction and are continuous around the apices ( Fig. 6E, F ). Distinct Voigt faults are present on the secondary side of the valve, located at 2/3 of the distance between the mid-valve and apex ( Fig. 6F ). The striae are not continuous and are interrupted by thickened vimenes along an apical orientation, except at the apices. The striae are covered with 4-6 rows of small multiseriate pores. Internally, the multiseriate pores are positioned between thickened virgae.

The linear-elliptic to linear-lanceolate with subcapitate to capitate shape and size of K. subtilissima matches K. neocaledonica Moser, Metzeltin & Lange-Bertalot , and K. krasskei Metzeltin & Lange-Bertalot , but the formation of the valve ends, and the central area are different.The interruption of the striae with vimenes between virgae (akin to Brachysira Kützing ) is distinct for this species which should be compared to Kobayasiella odakae (Skvortzov) Lange-Bertalot with a similar structural formation. Kobayasiella subtilissima is distinguished from K. odakae by a smaller valve surface depression around the central area, the presence of small projections off the virgae, and the more random disruption of the striae.

Figures

FIG. 2. — Light micrograph diminution series of Kobayasiella Lange-Bertalot species: A-P, Kobayasiella parasubtilissima (Kobayasi & Nagumo) Lange-Bertalot; Q-AB, Kobayasiella madumensis (Jørgensen) Lange-Bertalot; AC-AO, Kobayasiella subtilissima (Cleve) Lange-Bertalot. Scale bar: 10 µm.

FIG. 6. — SEM images of Kobayasiella subtilissima (Cleve) Lange-Bertalot:A, external view of the complete valve;B, internal view of the complete valve;C, external view of central area showing the multiseriate poroid covers between irregular formed virgae; D, internal view of the central area showing T-shaped proximal fissures and irregular orientated areolae;E, external view of the valve apex showing a partially curved proximal fissure opening into an elliptic surface depression; F, internal valve view of the apex. Helictoglossa expanded onto a highline apex. Areolae continue around the apex. Scale bars: A, B, 5 µm; C, 1 µm; D, F, 3 µm; E, 2 µm.

APPENDIX 3. — Relative abundance of species as a function of pH values.

APPENDIX 4. — Relative abundance of species as a function of DIC values.