Luticola bradyi Kohler, 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 : 120-122

Luticola bradyi Kohler , sp. nov. ( Figs. 84–91 )

LM observations ( Figs. 84–89 ): Valves elliptical to elliptical-lanceolate with convex margins. Apices broadly rounded, rostrate to sub-capitate. Valve dimensions (n=16): length 28.3–44.8 μm, width 10.5–12.5 μm. Axial area linear, slightly widening towards the valve center. An isolated pore present in the central area, located halfway between the valve center and valve margin. Central area asymmetric, varying from elliptic to an acute-angled sub-fascia, bordered by shortened striae on both sides, wider opposite the isolated pore. Raphe branches straight, deflected away from the isolated pore at both proximal and distal ends. Transapical striae radiate throughout, more widely spaced in the central portion of the valve, 16–18 in 10 μm. SEM observations ( Figs. 90–91 ): Externally, ( Fig. 90 ), striae composed of 5 – 7 areolae, 2 – 4 areolae at apices. Areolae rounded, slightly elongated along the axial and marginal areas and near poles, not extending past distal raphe endings. Isolated pore rounded, slightly elongated, Central area bordered by irregular, shortened striae comprised of 3–5 rows of five rounded areolae on isolated pore side, 1–2 rows on opposite side. Proximal raphe endings deflected opposite the isolated pore, resolving into small drop-like pores. Distal raphe endings slightly deflected opposite isolated pore, terminating into small pores or fissures on the valve face. Clear separation between valve face and margins with rounded mantle areolae interrupted at apices. A single row of rounded areolae present along entire valve mantle, interrupted at apices. Internally ( Fig. 91 ), central nodule thickened. Both, proximal and terminal raphe endings straight. Distal raphe ends terminating onto very small helictoglossae. Marginal canal visible, interrupted at apices. Areolae covered by hymens, forming continuous strip along striae. Isolated pore opening covered by solid silica flap.

Type:— ANTARCTICA. McMurdo Dry Valleys: Taylor Valley, Commonwealth Glacier, cryconite hole, Sample CC-9, A. Mass, 10 January 2014 (holotype INSTAAR! #2657A, illustrated in Fig. 88 , isotypes BM! 101776, BR! 4405).

Etymology:— This species is named for Brady Kohler (Cheney, Kansas, USA), brother and best friend of the first author.

Habitat, ecology and distribution:— Luticola bradyi has at present only been observed from the McMurdo Sound Region, Antarctic continent.A large population of L. bradyi was observed during a survey of the Commonwealth Glacier cryoconite holes collected during the austral summer 2013–14.This population was found among other common cryoconite species ( Stanish et al. 2013) such as Muelleria supra Spaulding & Esposito in Esposito et al. (2008: 1384, figs. 42–49), M. cryoconicola Stanish & Spaulding in Van de Vijver et al. (2010: 26, figs. 27–35), Humidophila spp . Lowe et al. (2014: 357), and L. gaussii ( Levkov et al. 2013: 117, pl. 127, figs. 1–19). Aside from this population, single valves have been recovered from Cape Royds, the Onyx River in Wright Valley, and streams in the Fryxell Basin, Taylor Valley.

INSTAAR herbarium:— Lake Fryxell 390; Canada Stream 436, 527, 618, 666–667, 670, 676, 683, 689, 691, 693–694, 696–697; Green Creek 512; Relict Channel 638, 640, 739, 751, 757; Von Guerard Stream 440–441; Commonwealth Stream 888; Coast Lake 2467; Commonwealth Glacier 2657.

Observations: — Previously referred to as L. cohnii var. #1 ( Esposito et al. 2008: 1381), this taxon was thought to be an initial cell of an unknown diatom due to its large size and scarcity. However, since a large population was found in a cryoconite hole on the Commonwealth Glacier, it is possible that this species is not rare, and is instead occasionally transported from the glaciers into streams. In valve dimensions and outline, L. bradyi most resembles L. wulffii (Peterson 1924: 312, fig. 2) Levkov et al. (2013: 259, pl. 126, figs. 19–29) which is an arctic species reported from Canada and Russia. However, L. wulffii has a very narrow rectangular to bow-tie shaped central area, while the central area in L. bradyi is broadly rectangular or elliptic. The shortened striae in L. wulffii are composed of 1–2(3) areolae ( Levkov et al. 2013), while the shortened striae in L. bradyi may number 3–5 on the side of the isolated pore. Striae in L. bradyi terminate more irregularly in the axial area than L. wulffii , which exhibits straight striae. Lastly, apices in L. bradyi are subcapitate at the largest sizes and become rostrate as valves become smaller.Apices in L. wulffii remain subcapitate, contricted where the apices meet the body, throughout the size range as illustrated in Levkov et al. (2013). These differences, along with opposite polar distributions, are sufficient to separate these two species from each other. Luticola magellanica (Frenguelli 1924: 95, pl. 6, fig. 37) Levkov et al. (2013: 153, pl. 41, figs. 12–19), described from Tierra del Fuego, is also similar in outline, but has denser striae (14–18 in 10 μm) and never develops constrictions at the apices; the apices are rounded.

In Antarctica, L. vermeulenii is similar in valve length and width range (24–50 μm, 9.5–14.0 μm), though slightly longer than our observed population of L. bradyi . Luticola vermeulenii also has denser striae (14–17 in 10 μm vs. 17–21 in 10 μm) and differs in valve outline, never forming constrictions at the apices like the subcapitate endings in L. bradyi at the upper size ranges. Another species that bears some resemblance based on valve outline and valve length, is L. vandevijveri Kopalová, Zidarova & Levkov in Levkov et al. (2013: 247, pl. 10, figs. 1–24), described from James Ross Island. The latter is however narrower (maximal width 9.0 μm) giving it a more slender outlook, and has a lower number of areolae per stria. In the McMurdo Sound Region, L. bradyi is most similar to L. spainiae and L. laeta , which are also common cryoconite species ( Stanish et al. 2013). However, most differences between these two species are found with respect to valve size. Luticola bradyi is generally much larger in length and width compared to L. spainiae and L. laeta , as well as most other Luticola . Lastly, the apices of L. bradyi are broadly rostrate, becoming subcapitate at larger size ranges. This differs from the apices of L. laeta , which are always more narrow and never become constricted where they meet the central area.

Figures

FIGURES 84–91. Luticola bradyi Kohler sp. nov. Light (LM) and scanning electron micrographs (SEM). 84–89. Specimens from Commonweath Glacier, Taylor Valley, the type population, LM. 90. External valve view, type population, SEM. 91. Internal valve view, type population, SEM. LM scale bar = 10 μm. SEM scale bars = 5 μm.