Luticola neglecta, Zidarova & Levkov & Vijver, 2014

Zidarova, Ralitsa, Levkov, Zlatko & Vijver, Bart Van De, 2014, Four new Luticola taxa (Bacillariophyta) from Maritime Antarctica, Phytotaxa 170 (3), pp. 155-168 : 157-158

Luticola neglecta sp. nov. ( Figs 2–20 )

Type:— ANTARCTICA. South Shetland Islands : Deception Island, Sample D 37, leg. R. Zidarova, coll. date 24/01/2013, slide no. BR- 4364 (holotype), slide PLP-253 (isotype University of Antwerp , Belgium), BRM-ZU9/67 (isotype BRM) .

Etymology:—The specific epithet refers to the fact that this species has been confused with other taxa and therefore neglected as a separate species (Latin: neglectus = neglected, overlooked).

Valves lanceolate to elliptic-lanceolate with convex margins and rounded apices. Valve length 7.3–18.2 µm, width 4.3– 5.4 µm. Axial area narrow, linear to linear-lanceolate. Raphe straight with weakly deflected proximal raphe endings and distal raphe fissures hooked towards the pore-bearing side. Central area with one isolated pore, bow-tie shaped, often asymmetrically enlarged, bordered on each side by 3–4 short striae. Striae moderately radiate in the middle, more radiate toward the apices, 21–26 in 10 µm.

Ecology and distribution:— Luticola neglecta has up to now only been observed on Deception Island in two samples, one collected from soil and one taken among almost dry moss, growing in a crack of coastal rocks under moderate nutrient input of birds and higher salinity levels due to the vicinity of the sea. Accompanying taxa included Pinnunavis gebhardii (Krasske) Van de Vijver in Van de Vijver et al. (2002: 77) and several other Luticola species. It is likely that the species is more widespread on the islands or even in Antarctica but it has been overlooked or misidentified in the past.

LM observations:— ( Figs 2–19 ): Larger valves are lanceolate with convex margins and weakly produced, rounded apices whereas smaller valves are more elliptic-lanceolate to even rhombic-lanceolate with convex margins and broadly rounded apices. Valve dimensions (n=24): length 7.3–18.2 µm, width 4.3–5.4 µm. The axial area is narrow, linear to linear-lanceolate, weakly widening towards the central area. The central area is enlarged into a bowtie shaped stauros, often asymmetrical because wider on the side opposite the isolated pore. In most valves, the central area is bordered on each side by 3–4 shortened striae composed of one single areola. One rounded isolated pore is present in the central area, located closer to the valve margin and not associated with a stria. The raphe is straight with almost inconspicuous proximal raphe endings that are weakly deflected opposite the isolated pore. The distal raphe fissures are visible in larger valves ( Figs 2, 4, 7, 8 ), elongated and hooked towards the pore-bearing side. The striae are moderately radiate in the valve middle, and become more radiate towards the apices, 21–26 in 10 µm.

SEM observations:— ( Fig. 20 ): The striae are composed of usually 2, occasionally 3 irregularly spaced, small, rounded to weakly transapically elongated areolae. The isolated pore is small and rounded. The proximal raphe endings are first weakly deflected opposite the pore-bearing side and then hook shortly towards the pore. Irregular, thread-like shallow depressions are present next to the proximal raphe endings. The distal raphe fissures are elongated and hooked towards the pore bearing side, reach the mantle and extend slightly onto it. One row of rounded areolae, interrupted at the valve poles, is present on the mantle.

Similar species:—A large number of Luticola taxa share a similar valve outline ( Table 1) but none of the already known species possesses the same unique combination of raphe structure, areolae and striation pattern present in L. neglecta . In LM L. neglecta can be confused with several typical Antarctic taxa: L. australomutica Van de Vijver in Van de Vijver & Mataloni (2008: 458), L. quadriscrobiculata Van de Vijver in Van de Vijver & Mataloni (2008: 457), L. pusilla Van de Vijver, Kopalová, Zidarova & Levkov in Levkov et al. (2013: 203) and L. delicatula Van de Vijver, Kopalová, Zidarova & Levkov in Levkov et al. (2013: 99). Luticola pusilla is easily separated by its broader valves with rather wide, lanceolate axial area, short distal raphe fissures that are weakly deflected opposite the pore-bearing side and lower number of striae ( Table 1). Luticola quadriscrobiculata , a species described from Deception Island ( Van de Vijver & Mataloni 2008), has larger valves with a relatively broad axial area and short, weakly deflected raphe fissures opposite the pore-bearing side, contrary to L. neglecta ( Table 1). Moreover, L. quadriscrobiculata typically has four pit-like depressions present in the central area, a feature never observed in L. neglecta . Both L. australomutica and L. delicatula have larger valve dimensions, short distal raphe fissures and a coarser striation pattern ( Table 1). The distal raphe fissures in L. neglecta are similar to those of the Antarctic L. nelidae Van de Vijver in Van de Vijver & Mataloni (2008: 458) but the latter has much larger and more linear-lanceolate valves with broader apices ( Table 1). Luticola simplex Metzeltin, Lange-Bertalot & García-Rodríguez in Metzeltin et al. (2005: 116), described from Uruguay, is similar in valve outline but has more rhombic-lanceolate valves with a larger valve width (> 5 µm), a lower number of striae and a different raphe structure, with the proximal raphe endings deflected opposite to the pore contrary to L. neglecta ( Table 1). Other similar taxa from around the world include Luticola imbricata (Bock) Levkov, Metzeltin & Pavlov in Levkov et al. (2013: 134) and L. pseudoimbricata Levkov, Metzeltin & Pavlov in Levkov et al. (2013: 193). Both taxa can be separated from L. neglecta by their proximal raphe endings that are turned opposite the isolated pore. Luticola imbricata also have a lower number of striae; L. pseudoimbricata possesses slit-like and not rounded isolated pore ( Table 1). L. pitranenis Levkov, Metzeltin & Pavlov in Levkov et al. (2013: 187), described from Macedonia, has larger rhombic valves, a lower stria density ( Table 1), a different raphe structure with more hooked proximal raphe endings and striae composed of 4–5 larger areolae, compared to the 2–3 small and rounded areolae in L. neglecta . Both Luticola intermedia (Hustedt) Levkov, Metzeltin & Pavlov in Levkov et al. (2013: 138) and L. frickei Levkov, Metzeltin & Pavlov in Levkov et al. (2013: 114) have larger valves with proximal raphe endings deflected or hooked opposite the pore-bearing side ( Table 1) and striae composed of more areolae (4–5 vs. 2–3). Another recently described taxon, L. minima Levkov, Metzeltin & Pavlov in Levkov et al. (2013: 157) has a comparable valve dimensions and striation pattern to L. neglecta ( Table 1), but again it can be separated by the proximal raphe endings that are deflected towards the side opposite the pore and not to the pore-bearing side. Finally, L. mutica has much longer proximal raphe endings, often hooked and even curved backwards, and a much lower stria density and larger valves, compared to L. neglecta ( Table 1) to exclude conspecificity.

Figures

FIGURES 2–20. Luticola neglecta Zidarova, Levkov & Van de Vijver, sp. nov. Light (LM) and scanning electron microscope (SEM) micrographs: Figs 2, 3–19. LM of 18 valves from the type population, Deception Island, sample D37 (scale bars = 10 µm). Fig. 20. SEM external view of a valve from the type population, Deception Island, sample D37 (scale bar = 5 µm).