Halamphora pertusa Stepanek & Kociolek, 2015

Kociolek, Patrick, 2015, Three new species of the diatom genus Halamphora (Bacillariophyta) from the prairie pothole lakes region of North Dakota, USA, Phytotaxa 197 (1), pp. 27-36 : 31

Halamphora pertusa Stepanek & Kociolek sp. nov. ( Figs 15–28 )

Valves are semi-elliptical, with a smoothly arched dorsal margin and a straight to slightly concave ventral margin. Valve length 17.0–34.0, valve breadth 5.0–6.0. Valve ends are protracted, narrowly rounded to sub-capitate and slightly bent ventrally. The raphe is arched, with straight raphe branches. Proximal raphe ends are straight to slightly dorsally deflected, the distal raphe ends are difficult to see in the LM. The axial area is narrow throughout, widening slightly near the ventral valve center. Dorsal striae are distinctly areolate, nearly parallel at the valve center, becoming radiate near the apices. Dorsal striae number 17–19 in 10 μm. Ventral striae are fine and number 29–31 in 10 μm.

In the SEM, externally, the raphe branches are straight with the proximal raphe ends slightly dorsally deflected and the distal ends hooked dorsally past the raphe ledge ( Figs 23, 24 ). The dorsal raphe ledge is prominent and is continuous the length of the valve. The dorsal striae are crossed by many irregularly spaces vimines, creating many internally biseriate round to ovoid areolae ( Fig. 25 , arrow). The ventral striae consist of a single row of elongate areolae. A marginal ridge is not present and the areolate striae continue uninterrupted to the valve margin. Internally, the dorsal striae appear irregularly biseriate throughout. A distinct longitudinal band of silica runs the length of the valve near the dorsal axial area ( Figs 27 arrow, 28).

Type: — USA. North Dakota, Kidder County: Salt Alkaline Lake , N46.95092°, W99.53915°, 3 November 2011, Holotype: Slide ANSP GC 65213 , Fig. 15 ; Isotypes: Cleaned material ANSP GCM 5691 , slide and cleaned material JPK 7977, Kociolek Collection at COLO .

Observations: — Halamphora pertusa is similar in valve outline and areolate striae to the freshwater species Halamphora punctata Stepanek & Kociolek (2013: 70) , and to the brackish/marine species Halamphora acutiuscula (Kützing) Levkov (2009: 167 ; basionym: Amphora acutiuscula Kützing 1844: 108 ) and Halamphora subholsatica (Krammer) Levkov (2009: 228 ; basionym: Amphora subholsatica Krammer 1997: 203 ). Halamphora pertusa can be distinguished from H. acutiuscula by its smaller size, longitudinal band of silica and the absence of distinctly thickened central dorsal virgae that is seen in H. acutiuscula ( Levkov 2009: pl. 234, Fig. 4 ). Halamphora pertusa shares the internal silica band with H. subholsatica , but can be distinguished by its smaller size, finer striation, closely spaced proximal raphe ends, straight to concave ventral margin and lack of any thickening of the dorsal central virgae ( Levkov 2009). Halamphora pertusa shares biseriate areolate striae with the freshwater species H. punctata , but can easily be distinguished by its comparatively broader valves, coarser striation, narrow ventral axial area and lack of any thickening of the dorsal central virgae ( Stepanek & Kociolek 2013).

Figures

FIGURES 15–22: LM. Halamphora pertusa sp. nov. Single valves showing size range. Fig. 15. Holotype specimen. Scale bar = 10 μm.

FIGURES 23–28: SEM. Halamphora pertusa sp. nov. Fig. 23. External whole valve view. Fig. 24. Detail of external valve apex. Fig. 25. Detail of the external areolae structure, showing internal biseriate sieve plate (arrow). Fig. 26. Interior whole valve view. Fig. 27. Detail of interior valve center showing longitudinal band of silica (arrow). Fig. 28. Detail of valve interior showing biseriate striae.

FIGURES 1–9: LM. Halamphora pratensis sp. nov. Single valves showing size range. Fig. 1. Holotype specimen. Scale bar = 10 μm.