Luticola transantarctica Kohler & Kopalová, 2015

Kohler, Tyler J., Kopalová, Kateřina, Vijver, Bart Van De & Kociolek, J. Patrick, 2015, The genus Luticola D. G. Mann (Bacillariophyta) from the McMurdo Sound Region, Antarctica, with the description of four new species, Phytotaxa 208 (2), pp. 103-134 : 128-130

Luticola transantarctica Kohler & Kopalová , sp. nov. ( Figs. 142–151 )

LM observations ( Figs. 142–148 ): Valves elliptic-lanceolate, becoming slightly rhombic in larger specimens ( Figs. 142– 143 ). Margins symmetrical, convex and rounded in central area. Apices broadly rounded, capitate, becoming slightly rostrate in smaller specimens ( Fig. 148 ). Valve dimensions (n=25): length 16.0–50.9 μm, width 7.1–10.6 μm. Axial area narrow, expanding towards central area. An isolated pore present in central area, located halfway between valve center and valve margin. Central area rectangular to elliptical, bordered by shortened striae on both sides. Raphe branches straight with both proximal and distal endings slightly deflecting away from isolated pore. Transapical striae radiate throughout, 18–22 in 10 μm. SEM observations ( Figs. 149–151 ): Externally ( Fig. 150 ), striae composed of 3–5 areolae, 2–3 at apices. Areolae round- ed to elongated throughout, extending to the distal raphe endings. Isolated pore appears slightly elongated, but obscured by debris. Central area bordered by 1–2 rows of three rounded areolae on the isolated pore side, and a single row on the opposite side. Proximal and distal raphe endings slightly deflected opposite isolated pore, terminate on valve face. Clear separation between valve face and margins. A single row of rounded areolae visible along valve mantle, interrupted at apices. Internally ( Figs. 149, 151 ), structures difficult to discern due to specimen corrosion and small sample size. Central nodule thickened. Distal raphe endings straight, proximal raphe endings deflect slightly towards isolated pore.

Type:— ANTARCTICA, McMurdo Dry Valleys, Wright Valley, Labyrinth Pond, Sample #4, A. Sakaeva, 07 January 2014 (holotype INSTAAR! #2669A, illustrated in Fig. 145 , isotypes BM! 101779, BR! 4408).

Etymology:— The name “ transantarctica ” is in reference to the isolated locality in which the type population was collected from; The Labyrinth, Wright Valley, at the foot of the Transantarctic Mountains.

Habitat, ecology and distribution:— At present, this species is only known from The Labyrinth in Wright Valley, Antarctica, where it comprised over 60% of the diatom community by relative abundance ( Sakaeva 2014).

INSTAAR herbarium:— Labyrinth Pond 2669.

Observations:— If observed at all, the lower size range of this taxon may have previously been identified as L. muticopsis f. reducta because of images published by Kellogg et al. (1980), which appear to show the reduced form of L. gaussii or other Luticola with rounded apices. Like N. muticopsis f. evoluta , there is no original illustration for L. muticopsis f. reducta , and the description is limited to “Cells are shorter, poles less drawn out and distinctly truncated, striae 13 in 10 μ” (translated from Latin, West & West 1911: 284). However, since L. transantarctica was not was not observed in our survey of Cape Royds, nor in the original West & West (1911) slides, we conjecture that the two are not conspecific. Based on published images, it is also possible that L. transantarctica has been observed in the past and identified as L. murrayi ( Kellogg et al. 1980: 176, pl. 1, fig.20) or Naviula globiceps f. amphicephala ( Ko-Bayashi 1963: 13, pl. 4, fig. 3), but these populations should be re-investigated before this can be said for certain.

From the Antarctic continent, Luticola transantarctica is most similar in morphology to L. pseudomurrayi , described from Langhovde, Lützow Holm Bay, East-Antarctica ( Van de Vijver et al. 2012). However, L. transantarctica differs from L. pseudomurrayi by having more capitate apices, with narrower constrictions between the apices and the valve center. Lastly, L. pseudomurrayi has a larger upper width range than L. transantarctica (7.5–12.0 μm vs. 7.1– 10.6 μm). From the McMurdo Sound Region, L. transantarctica could be confused with L. elegans , especially at the lower end of the size range. However, apices in L. transantarctica remain capitate at small sizes, whereas in L. elegans they become more rostrate at lower as well as greater sizes. Luticola gaussii is very similar in valve outline, especially at intermediate lengths. However, L. gaussii has a more rounded central area compared to the elliptic central area in L. transantarctica , and L. gaussii additionally has slitted punta under SEM. Furthermore, the striae of L. gaussii are patterned as noted by West & West (1911), with two lines running along the axial area in the valve center and one at the apices. In L. transantarctica , striae form no such pattern, are punctate and irregular. Finally, L. gaussii is consistently wider than L. transantarctica at any given length.

Figures

FIGURES 142–151. Luticola transantarctica Kohler & Kopalová, sp. nov. Light (LM) and scanning electron micrographs (SEM). 142– 148. Specimens from the Labyrinth Pond, Wright Valley, the type population, LM. 149. Detail of isolated pore, internal valve view, SEM. 150. External valve view, type population, SEM. 151. Internal valve view, type population, SEM. LM scale bar = 10 μm. SEM scale bars = 10 μm, 4 μm for detail of internal isolated pore.