Luticola macknightiae 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 : 126-128

Luticola macknightiae Kohler & Kopalová , sp. nov. ( Figs. 121–141 )

LM observations ( Figs. 121–138 ): Valves linear-lanceolate to elliptical-lanceolate, with convex, sometimes slightly undulate margins ( Figs. 122–123 ). Apices irregular protracted, nearly round, truncate to rostrate at smaller sizes ( Figs. 130–138 ). Valve dimensions (n=24): length 6.7–29.5 μm, width 4.3–7.8 μm. Axial area linear, widening towards the central area. An isolated pore present in the central area, located halfway between valve margin and valve center. Central area broadly elliptical, bordered on both sides by shortened striae. Raphe branches straight, with proximal and distal endings deflected opposite the isolated pore. Distal raphe endings short, terminating on the valve face well before apices. Transapical striae radiate throughout, 16–21 in 10 μm. SEM observations ( Figs. 139–141 ): Externally ( Fig. 139 ), striae composed of 2–3 areolae, 1–2 at apices. Areolae rounded, elongated near valve margin, extend well past distal raphe endings before terminating almost on valve margin ( Fig. 141 ). Isolated pore rounded. Central area bordered on both sides by a single row of 3–4 rounded areolae positioned closer to the valve margin than other striae. Proximal raphe endings deflected opposite side of isolated pore, terminating into small open pores. Distal raphe endings straight, slightly deflected away from isolated pore, terminating into small fissures on the valve face distinctly before apices. Clear separation between valve face and margin, with clear open area at apices. A single row of rounded areolae visible along entire valve mantle. Internally ( Fig. 140 ), central nodule thickened. Marginal canal well developed, clearly visible in central area, interrupted at the apices. Areolae covered by hymenes, forming continuous a strip along each stria. Isolated pore opening covered by solid silica flap.

Type:— ANTARCTICA. McMurdo Dry Valleys: Taylor Valley, Wormherder Creek microbial mat, Sample WHC11-2, T. J. Kohler, 10 January 2012 (holotype INSTAAR! #958A, illustrated in Fig. 125 , isotypes BM! 101778, BR! 4407).

Etymology:— Luticola macknightiae is named in honor of our advisor, colleague, and friend, Dr. Diane McKnight (University of Colorado, Boulder, USA), who has promoted a better understanding of freshwater ecosystems through her research in the McMurdo Dry Valleys.

Habitat, ecology and distribution:— At present, L. macknightiae is only known from the McMurdo Dry Valleys. As it has been previously been identified as L. muticopsis f. evoluta ( Esposito et al. 2006, 2008, Spaulding et al. 2010, Stanish et al. 2011, 2012), its distribution is known to be widespread throughout the MDVs, occupying stream microbial mats and mosses. It is especially abundant in the Lake Bonney Basin streams, where it sometimes comprises half of the communities by relative abundance ( Stanish et al. 2012).

INSTAAR herbarium:— Aiken Creek 900, 2227; Von Guerard Stream 906–907, 911–912, 916–917, 919, 923– 926; Harnish Creek 928; Bowles Creek 933, 936, 938, 940; Commonwealth Stream 945, 948; Wormherder Creek 955, 958; Priscu Stream 960–961; Bohner Stream 963–966; McKay Creek 975, 977; Wharton Creek 979–980, 982; Delta Stream 983–984, 986–987, 990–992; Onyx River 995–996, 999; Canada Stream 1003, 1011, 2257; Green Creek 1018–1019, 1021–1022, 1025, 1027; Lawson Creek 1030, 1032–1033; Miers Stream 1049; Adams Stream 1051– 1054, 1064; Relict Channel 1068, 1070, 1077–1081, 1084, 1087; Little Sharpe (unofficial name) 2340; Lyons Stream tributary 2349–2351; Spaulding Pond 2495–2496; Blue Lake 2498; Clear Lake 2501; McMurdo Hut Ridge 2665; Picture Pond 2667–2670; Nussbaum Regal Pond (unofficial name) 2671, Upland Pond 2677–2678.

Observations:— The identification of L. macknightiae as N. muticopsis f. evoluta probably originates with the publication by Ko-Bayashi (1965: pl. 31), where a small Luticola with almost rostrate apices is depicted as this form. Since there is no illustration of N. muticopsis f. evoluta in West & West (1911), and the original description is limited to “Cells are slightly elongated, slightly below the pole, each distinct but slightly constricted; striae 13–14 in 10 μm” (translated from Latin, West & West 1911: 283), it is entirely impossible to match this form with any extant species. Because of this, N. muticopsis f. evoluta has previously been identified as what is the current concept for L. austroatlantica ( Kellogg 1980: 176, pl. 1, fig.11), L. pseudomurrayi ( Ko-Bayashi 1963: pl. 8, figs. 1–2), and the reduced form of various unknown diatoms ( Ko-Bayashi 1965: pl. 29). Furthermore, in our investigation of the recent Cape Royds material, as well as the original slides from Shackleton’s expedition, we found no valves resembling L. macknightiae , although West & West (1911: 284) stated that N. muticopsis f. evoluta was “…common over the whole area in which collections were made”. Because of its absence, we conclude the two are not conspecific, and we describe L. macknightiae as a new species.

Luticola macknightiae most resembles L. vesnae Levkov in Levkov et al. (2013: 254, pl. 15, figs. 5–6, and pl. 157, figs. 13–21) valve outline. Described from Macedonia, L. vesnae is similar in size, measuring 17–34 μm long and 5.3–8.0 μm wide ( Levkov et al. 2013). However, it has more dense striae (22–24 in 10 μm), more areolae per stria (3 or 4), and external distal raphe endings continue onto valve mantle, whereas in L. macknightiae the raphe terminates at or before the last row of areolae. Among Antarctic taxa, L. macknightiae shares similarities to L. delicatula Van de Vijver, Kopalová, Zidarova & Levkov in Levkov et al. (2013: 99, pl. 53, figs. 21–26, pl. 54, fig. 6), though this species is wider (7.0–9.0 μm), has more coarse striae (15–16 in 10 μm), and is generally widest in the center of the valve tapering to rounded apices. This is in contrast to L. macknightiae which has two convex margins and rostrate apices. Luticola macknightiae may also resemble L. pusilla Van de Vijver, Kopalová, Zidarova & Levkov in Levkov et al. (2013: 203, pl. 50, figs. 1–16, pl. 51, figs. 1–7) in dimensions; L. pusilla is 12–28 μm long, 4.5–7.5 μm wide, and has 18–21 striae in 10 μm composed of 2–3 areolae. It differs from L. macknightiae in having more rounded apices and a more oval shaped intermediate size range. Furthermore, L. pusilla has a widened distal end of the raphe not present in L. macknightiae ( Levkov et al. 2013) .

On continental Antarctica, L. macknightiae may only be confused with L. austroatlantica because both taxa have convex margins and at intermediate size ranges exhibit rostrate apices. However, L. austroatlantica has distinctly capitate apices at upper size ranges and are more parallel where they meet the central are in intermediate size ranges resulting in distinct “shoulders”. In L. macknightiae , apices are rostrate at intermediate sizes, and are never fully capitate at upper size ranges. In addition, the areolae of L. macknightiae are more sparsely distributed within striae (2–3) compared with L. austroatlantica (3–4). Lastly, L. macknightiae is consistently narrower than L. austroatlantica at any given length, making comparisons between populations straightforward.

Figures

FIGURES 121–141. Luticola macknightiae Kohler & Kopalová, sp. nov. Light (LM) and scanning electron micrographs (SEM). 121– 138. Specimens from Wormherder Creek, Taylor Valley, the type population, LM. 139. External valve view of a specimen from Canada Stream, Taylor Valley, SEM. 140. Internal valve view of a specimen from Canada Stream, SEM. 141. Detail of apices from Canada Stream specimen, SEM. LM scale bar = 10 μm. SEM scale bars = 2 μm for inside/outside, 5 μm for detail of external apice.