Iconographia Diatomologica 6: 267 (Lange-Bertalot 1999). — Navicula madumensis JØrgensen, Det Kongelige Danske Videnskabernes Selskab, Biologiske Shrifter 5 (2): 60 (JØrgensen 1948). — Kobayasia madumensis (JØrgensen) Lange-Bertalot, Iconographia Diatomologica 4: 282 (Lange-Bertalot 1996).
ECOLOGY AND DISTRIBUTION. — Kobayasiella madumensis was found in four lakes in this study, never exceeded 1% relative abundance and had no evident ecological preferences. In North America, Camburn & Charles (2000), Metzeltin & Lange-Bertalot (2007) and Siver & Hamilton (2005) reported this species in low alkaline and low pH lakes from the eastern part of the continent.
The frustules have a rectangular and narrow shape in girdle view. The valves are linear-elliptic with more or less capitate protruding ends. Based on a sample size of 15, the valve dimensions range from a length of 29.5 to 37 µm and a width of 5.5 to 7 µm, with the length-to-width ratio from 4.8 to 5.5 µm. The stria density ranges from 37 to 40 in 10 µm. The axial area is lanceolate and narrow, and in LM, it is almost indistinct. The central area is small and apically linear-elliptic, with 9-10 marginal striae of varying lengths aligned between the proximal raphe ends. The external valve face is flat. The raphe is linear, with a kink-like irregularity halfway between the mid-valve and apex. Externally, the central raphe fissures are linearly expanded, with a teardrop-shaped proximal fissure. The terminal raphe fissures are bent but not hooked, directed towards the secondary side of the valve (Fig. 5F). There is a slightly raised terminal nodule with a terminal axial area. Internally, the raphe is located on a thickened sternum and appears straight, without a kink-like irregularity. The proximal raphe fissures are close together, small, and Y-shaped to T-shaped, with surrounding ridges on the sternum (Fig. 5D, E). The terminal fissures end on raised elongated helictoglossae, isolated from the apex mantle (Fig. 5G). The striae are strongly radiate at the mid-valve and become strongly convergent at the apices. From the mid-valve to the Voigt fault, the individual striae change from straight to bent, and from the Voigt fault to the apex, the striae change from bent to straight. The mantle striae are interrupted by a thick hyaline ridge at the valve face/mantle junction and are not continuous around the apices (Fig. 5F). 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. Externally, the striae are covered with two rows of small pores. Internally, the biseriate pores are positioned between thickened virgae. Additionally, the striae around the central area are narrow and transapically elongated.
The broader linear-elliptic valve with capitate ends distinguishes this taxon from most Kobayasiella species including truly broad taxa such as K. lange-bertalotii Metzeltin and K. krasskei Metzeltin & Lange-Bertalot. A closely related valve form includes K. subtilissima sensu Germain (1981; not K. subtilissima sensu stricto), however distinct differences between the Germain specimen and K. madumensis are evident with a smaller distance between the central raphe ends and no expanded central area. Kobayasiella pseudosubtilissima (Manguin) Lange-Bertalot is similar in outline, but K. madumensis is distinguished from the former taxon by the small, less curved terminal raphe fissures, the capitate (not rostrate) ends and the higher stria density (37-40 vs 30-32 in 10 µm). JØrgensen first documented a lanceolate taxon with head-shaped extremities (K. madumensis) from Madum SØ, Denmark. The original line drawing does not match the current concept of the species, which was established using the examination of type-prep material collected by JØrgensen (HER Nr. 69) (Lange-Bertalot 1996). In this examination Lange-Bertalot reports a linear-elliptic valve similar to that observed in North America. Siver et al. (2005) illustrate LM and SEM of K. madumensis specimens from Cape Cod (United States) that match specimens from Tursujuq National Park.