Nupela mongolica
sp. nov.
The new species
Nupela mongolica
sp. nov. most closely resembles
N. fennica (Hustedt) Lange-Bertalot (2004: 440)
. Both species have a well developed raphe system on both valves. The shape of the central and axial areas of these species is also similar, the central area is represented by a fascia bordered by areolae, the axial area is narrow linear. However, the species differ by valve shape:
N. mongolica
sp. nov. has linear valves with parallel margins and broadly rounded ends ( Figs 2–15
View FIGURES 2–15
), while valves of
N. fennica
are linear-lanceolate to linear-elliptic, with subrostrate to rounded ends (see Table 1). The valves of
N. mongolica
sp. nov. are generally narrower than
N. fennica
(width 2.7–3.0 µm). The central area in
N. mongolica
sp. nov. is bordered by 7–10 very short striae on both sides of the valve, in
N. fennica
it may be bordered only on one side ( Simonsen 1987, Pl. 728, figs 33–35; Potapova 2011, figs 6, 7; Buczkó et al. 2013, figs 2–4). The species also differ by striae density (40–44 in 10 µm in
N. mongolica
sp. nov. vs. 35–40 in 10 µm in
N. fennica
).
N. mongolica
sp. nov. is also similar to
N. subrostrata (Hustedt) Potapova (2011: 83)
in regards to valve shape. The valves of
N. mongolica
sp. nov. are linear, which was also shown for
N. subrostrata
( Potapova 2011, figs 19–22). The most important difference between these species is the raphe system organization type.
N. mongolica
sp. nov. is a biraphid taxon, whereas in
N. subrostrata
the raphe system is absent on one of the valves. The axial area in
N. mongolica
sp. nov. is very narrow, linear, weakly widened near the central area, while in
N. subrostrata
the axial area on the raphe valve is small, of variable shape, from symmetrical to asymmetrical (see Table 1). The valve ends in
N. mongolica
sp. nov. are broadly rounded, in
N. subrostrata
they are slightly protracted ( Potapova 2011, figs 19–27). The quantitative features also differ in these two species: the valves of
N. mongolica
sp. nov. are narrower (valve width 2.4–3.0 µm vs. 3.4–5.1 µm in
N. subrostrata
), and the striae density in the new species is higher (40–44 in 10 µm vs. 20–24 in 10 µm in
N. subrostrata
) (see Table 1).
Some valves of
N. silvahercynia (Lange-Bertalot) Lange-Bertalot
in Lange-Bertalot & Metzeltin (1996: 97) described in literature resemble
N. mongolica
sp. nov. in outline (see, e.g., Krammer & Lange-Bertalot 1989, Taf. 71, fig. 34; Lange-Bertalot & Metzeltin 1996, taf. 22, figs 55; 56; Potapova 2014, fig. 217). Nevertheless, in general the valves of
N. silvahercynia
range in shape from linear-elliptic to linear-elliptic-lanceolate with rounded ends (Krammer & Lange-Bertalot 1989, Taf. 71, figs 33–37), while the valves of
N. mongolica
sp. nov. are linear ( Figs 2–15
View FIGURES 2–15
). In both species the axial area is narrow linear, slightly widening towards the central area (see Table 1). However, as the previous species included in this comparison,
N. subrostrata
,
N. silvahercynia
is a heterovalvar species (see Table 1). The central area in
N. mongolica
sp. nov. has the form of a fascia bordered on both sides by 7–10 very short striae, while in
N. silvahercynia
the central area on the raphe valve is rectangular to elliptical, and on the rapheless valve the axial area is asymmetrically widened (Krammer & Lange-Bertalot 1989, Taf. 71, figs 33–37).
N. silvahercynia
has rounded external openings of the areolae ( Potapova 2014, fig. 238); in
N. mongolica
sp. nov. they are clearly transapically elongated ( Figs 22–26
View FIGURES 21–26
). The species can also be differentiated by qualitative features like valve width (2.4–3.0 µm in
N. mongolica
sp. nov., 3.0–3.8 µm in
N. silvahercynia
) and striae density (40–44 in 10 µm in
N. mongolica
sp. nov., 31–33 in 10 µm in
N. silvahercynia
) (see Table 1).
N. mongolica
sp. nov. forms an individual branch with high statistical support that is sister to strains of
N. indonesica
and
N. lesothensis
; the two species are more closely related to each other than to the new species. Morphologically
N. mongolica
sp. nov. is not similar to the other species (Kulikovskiy et al. 2020).
