Luticola spainiae 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 : 122-126

Luticola spainiae Kohler & Kopalová , sp. nov. ( Figs. 92–109 )

LM observations ( Figs. 92–107 ): Valves elliptical to elliptical-lanceolate with two convex margins. Apices rounded at the lower size range ( Figs. 100–101 ), broadly rostrate to sub-capitate at upper sizes ( Figs. 92–99 ). Valve dimensions (n=22): length 12.1–33.6 μm, width 6.4–8.7 μm. Axial area linear, slightly widening towards the central area. An isolated pore present in the central area, located halfway between the valve center and valve margin. Central area bow-tie shaped to almost rectangular, bordered on both sides by shortened striae. Raphe branches straight, deflected away from the isolated pore at both proximal and distal ends. Transapical striae irregular, radiate throughout entire valve, 19–22 in 10 μm. SEM observations ( Figs. 108–109 ): Externally ( Fig. 108 ), striae composed of 4–5 areolae, 2–4 at apices. Areolae rounded, becoming slightly elongated near axial area and at poles, extending beyond distal raphe endings. Isolated pore small, rounded. Central area bordered by 2–3 rows of four rounded areolae on isolated pore side, and a single row of four on opposite side. Proximal and distal raphe endings open drop-like pores and deflect away from isolated pore. Distal raphe endings terminate on the valve face. Clear separation between valve face and margins. Internally ( Fig. 109 ), central nodule thickened. Both proximal and distal raphe endings straight. Distal raphe endings terminating onto very small helictoglossae. Marginal canal visible, interrupted at apices. Areolae covered by hymenes, forming a continuous strip along each stria. Isolated pore opening covered by solid silica flap.

Type:— ANTARCTICA. McMurdo Dry Valleys: Fryxell Lake Basin, Commonwealth Glacier, cryconite hole, Sample CC-9, A. Mass, 10 January 2014 (holotype INSTAAR! #2657A, illustrated in Fig. 95 , isotypes BM! 101777, BR! 4406).

Etymology:— Luticola spainiae is named in honor of our friend and colleague, Rae Spain, whose years as the Lake Hoare camp manager have facilitated decades of research in the McMurdo Dry Valleys in addition to providing visitors a home away from home.

Habitat, ecology and distribution:— Luticola spainiae is at present known only from the Commonwealth Glacier cryoconite holes, Taylor Valley, Antarctic continent. Found alongside L. bradyi as well as other common cryoconite species, such as Muelleria supra , M. cryoconicola , M. peraustralis (W. & G.S. West 1911: 284) Spaulding & Stoermer in Spaulding & Stoermer (1997), Humidophila spp ., and L. gaussii ( Stanish et al. 2013) . Due to similarities with L. laeta , L. mutica , and L. bradyi , this species may be under-reported from the McMurdo Sound Region.

INSTAAR herbarium:— Commonwealth Glacier 2657

Observations: — If observed at all, the smaller size range of this species has probably been identified as L. mutica or L. cohnii , which may be a complex similar to L. muticopsis in Antarctica ( Van de Vijver & Mataloni 2008). Like the lower size range of L. spainiae , L. mutica is oval-shaped, but the latter has eccentric proximal raphe endings terminating in hooks ( Levkov et al. 2013: 284, pl. 2, figs. 1–8), which is visible under SEM. Furthermore, at the upper size ranges, L. spainiae has distinctly rostrate apices not present in L. mutica , and reaches a greater upper size (vs. 28 μm for L. mutica ). Luticola cohnii is another diatom reported from the Antarctic continent that resembles L. spainiae in valve outline, especially at lower size ranges. However, L. cohnii is in general longer (19–40 μm) and wider (8.5–11.0 μm) than L. spainiae ( Levkov et al. 2013: 91) . Furthermore, L. cohnii is always oval in outline even at large sizes, while valve apices become rostrate in L. spainiae . Furthermore, the eccentric distal raphe endings in L. cohnii terminate on valve margins, whereas in L. spainiae , they terminate on the valve face ( Levkov et al. 2013: 292, pl. 6, figs. 1–8).

Other Antarctic diatoms such as L. vermeulenii ( Van de Vijver et al. 2011: 145, figs. 16–29) may be similar in valve outline, but have a greater length and width range (24–50 μm, 9.5–14.0 μm). Luticola vermeulenii also has denser striae (14 – 17 in 10 μm vs. 19 – 22 in 10 μm) and differs in valve outline, never forming constrictions at the apices like the subcapitate endings in L. spainiae at upper size ranges. In the MDVs, L. spainiae is very similar in valve outline to L. bradyi , which is found in the same cryoconites. The major difference between these species is the width of valves. The upper end of the L. spainiae width range is 8.7 μm, while the lower width range of observed L. bradyi is 10.5 μm. Distal and proximal raphe pores are much larger in this species than in L. bradyi , which actually has a proximal raphe that resolves into slits. Also very similar is L. laeta , and it is possible that confusion between these two species has taken place in the past, as they are almost identical in their length/width ratios. However, L. spainiae has much broader, more rostrate apices than L. laeta , and has more areolae per striae, especially with regard to the shortened striae near the isolated pore in the central area, which only numbers 1–2 in L. laeta .

Luticola elegans (W. & G.S.West) Kohler & Kopalová, comb. nov. stat. nov. ( Figs. 110–120 , Fig. 110 is original illustration by West & West (1911))

Basionym: Navicula (Pinnularia) murrayi var. elegans W. & G.S. West (1911) British Antarctic Expedition 1907 –1909, vol. 1., Biology, Part VII, p. 285, pl. XXVI, fig. 130).

LM observations:— ( Figs. 111–118 ) Valve lanceolate to elliptical-lanceolate with two convex margins.Apices capitate to sub-capitate in middle size ranges ( Figs. 112–115 ), becoming rostrate in smaller and greater size range ( Figs. 111, 116–118 ). Valve dimensions (n=10): length 12.9–35.8 μm, width 6.4–9.5 μm. Axial area linear, widening slightly towards central area. An isolated pore is present in the central area, located halfway between the valve margin and valve center. Central area broadly rectangular to round, bordered by shortened striae on both sides. Raphe branches straight, both proximal and distal raphe endings deflected away from the isolated pore. Transapical striae irregular, radiate throughout, 16–20 in 10 μm.

SEM observations:— ( Figs. 119–120 ) Externally ( Fig. 119 ), striae composed of 3–4 areolae, 2–3 at apices.Areolae rounded throughout, becoming elongated at margins near central area, extend to the distal raphe ending. Isolated pore elongated, slit-like. Central area bordered by a single row of 3–4 rounded areolae on both sides, positioned closer to the valve margin than other striae. Distal raphe endings deflect away from isolated pore on a valve face, resolving into slits. Proximal raphe ending terminates in slightly opened pore, deflected away from isolated pore. Clear separation between valve face and margins, with open area at apices around terminal raphe endings. A single row of areolae visible in a shallow depression along entire valve mantle. Internally ( Fig. 120 ), structures difficult to discern due to specimen corrosion and small sample size.

Habitat, ecology and distribution:— Luticola elegans is known only from Cape Royds and the McMurdo Dry Valleys. Since this species has probably been identified as both L. muticopsis and L. austroatlantica due to similarities in morphology and extensive varieties present in L. muticopsis (i. e. Ko-Bayashi 1963, 1965), its distribution may be more widespread than currently known. Sakaeva (2014) report it from many of the upland ponds from both Cape Royds and the MDVs, and we can confirm its presence in at least Wales and Crescent streams. The basionym, Navicula murrayi var. elegans , has been reported from Graham Land ( Carlson 1913), Ongul Islands ( Ko-Bayashi 1963), and South Shetland Islands ( Carlson 1913), though these distributions should be interpreted with caution.

INSTAAR herbarium:— Green Lake 2475; Spaulding Pond 2495–2496; Blue Lake 2497–2499; Clear Lake 2501; McMurdo Hut Ridge 2664–2665; Picture Pond 2666–2668, 2670; Nussbaum Regal Pond (unofficial name) 2671; Upland Pond 2677–2678; Hughes Glacier Pond (unofficial name) 2679.

Observations:— West & West (1911) described Navicula murrayi var. elegans from presumably one large valve measuring 31 μm long, 8.1 μm wide, and with 15 striae per 10 μm. Later, Ko-Bayashi (1963: pl. 8, figs. 3 – 4) published images of what may be this diatom under the name N. muticopsis var. elegans , but it has been seldom reported since. In our survey of recent material at Cape Royds, we found a species that we argue belongs to N. murrayi var. elegans due to the strong morphological resemblance of the upper size range to the original illustration, as well as the locality from which our samples were taken. As a result, we here elevate the Cape Royds taxon to a species of Luticola . Levkov et al. (2013) report a species that may be conspecific from Cape Royds as L. murrayi , and has a length 16–35 μm, width 6.5 – 8.5 μm, and 15–17 striae in 10 μm. The authors also report initial cells up to 45 μm long and 12 μm wide. While we did not measure any initial cells of this length when analyzing the Mt. Erebus Moraine slides (including the lectotype, BM 34126), we did photograph one initial cell from BM 34124, and have included it as Fig. 57 for reference.

The upper size range of this species may be confused with L. murrayi , and is probably why this species was initially described as a variety. However, when a size diminution series of each species is observed and compared, they can be easily separated into two morphologically distinct groups. The morphology of L. elegans includes strongly capitate ends at intermediate size range, becoming more rostrate at the upper and lower size ranges. Apices of Luticola murrayi on the other hand never become capitate nor rostrate at upper or lower size ranges, and remain obtuse and rounded in all cells. Furthermore, the center of the valve remains rounded and convex in L. elegans , conforming well to the description of Navicula murrayi var. elegans reported by West & West (1911: fig. 130), while the widest part of L. murrayi is directly in the center of the cell. Lastly, the central stauros in L. elegans can be rounded (though it can also be rectangular) unlike L. murrayi , and is clearly illustrated in the original West & West (1911: fig. 130) illustration.

Luticola elegans may be confused with L. austroatlantica , which is very similar in valve outline at intermediate side ranges. However, L. austroatlantica is more narrow in width (5.6–8.2 μm vs. 6.4–9.5 μm), and has fewer areolae per striae (2–3 vs. 3–4). Luticola elegans additionally is less constricted between the capitate apices and the valve center compared to L. austroatlantica , and apices are generally wider. At the upper size range, L. elegans is more rostrate, while L. austroatlantica is more capitate. Conversly, L. austroatlantica is more rostrate at lower size ranges, while L. elegans has sub-capitate apices even at the smallest sizes. Luticola elegans may also resemble L. gaussii , and the two are often found in the same habitats, especially at Cape Royds. However, L. gaussii differs in valve outline, having a more rounded central portion while L. elegans is more elongate. In general, L. gaussii is wider and shorter than L. elegans , and L. gaussii additionally has more dense (19–23 in 10 μm), patterned striae organized into three longitudinal rows not present in L. elegans .

Figures

FIGURE 57. Initial cell from BM 34124, an original West & West (1911) slide, LM. Scale bar = 10 μm.

FIGURES 92–109. Luticola spainiae Kohler & Kopalová, sp. nov. Light (LM) and scanning electron micrographs (SEM). 92–107. Specimens from Commonwealth Glacier, Taylor Valley, the type population, LM. 108. External valve view, type population, SEM. 109. Internal valve view, type population, SEM. LM scale bar = 10 μm. SEM scale bars = 5 μm.

FIGURES 110–120. Luticola elegans (W. & G.S.West) Kohler & Kopalová, comb. et stat. nov. 109. Original illustration from West & West (1911: pl. 26, fig. 130). Light (LM) and scanning electron micrographs (SEM). 111–118. Specimens from Green Lake, Cape Royds, LM. 119. External valve view of a specimen from Green Lake, SEM. 120. Internal valve view of a specimen from the Nussbaum Riegal, SEM. LM scale bar = 10 μm. SEM scale bars = 5 μm.