Halamphora pratensis 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 : 28-29

Halamphora pratensis Stepanek & Kociolek sp. nov. ( Figs 1–14 )

Valves are semi-elliptical with a smoothly rounded dorsal margin and a straight to slightly concave ventral margin, the ventral margin in larger specimens is often slightly tumid. Valve length 13.0–35.0 μm, valve breadth 4.5–6.0 μm. Valve ends are protracted, narrowly rounded and slightly bent ventrally. The raphe is arched with nearly straight raphe branches. Proximal raphe ends are straight and the distal raphe ends deflect dorsally. The axial area is narrow throughout. Dorsal striae are areolate, slightly radiate throughout, becoming more so near the apices. Dorsal striae are distinctly more widely spaced near the valve center, with 23–27 striae in 10 μm and 31–34 in 10 μm near the apices. Ventral striae are difficult to see in the LM. A dorsal marginal ridge is not apparent.

In the SEM, externally, the raphe is straight with proximal ends straight to slightly deflected dorsally and the distal ends are weakly deflected dorsally. The dorsal raphe ledge is small and continuous across the length of the valve, ending before the proximal raphe ends ( Figs 10, 12 ). The axial area is narrow on the dorsal side, more pronounced on the ventral side and expanded near the valve center. The dorsal striae are separated by thin virgae and are crossed, externally and internally, by thick irregularly placed vimines creating round to ovoid areolae of varying size. The dorsal virgae are thickened near the valve center, a feature that is more pronounced internally ( Fig. 13 , arrow). The dorsal marginal ridge is variable. Externally, the ridge is well defined only near the apices, where it wraps around the distal raphe end to merge with the ventral margin ( Fig. 12 , arrow), but becomes much less defined over the central portion of the valve. The ventral striae are difficult to see externally due to their marginal position, but can be observed internally as a single continuous row of elongate areolae. The girdle area consists of six bands, each having two rows of elongate areolae running their length ( Fig. 14 ).

Type: — USA. North Dakota, Burleigh County: Long Lake , N46.69169°, W100.19026°, 3 November 2011, Holotype: Slide ANSP GC 65212 , Fig. 1 ; Isotypes: Cleaned material ANSP GCM 5690 , slide and cleaned material JPK 7951, Kociolek Collection at COLO .

Observations: — Halamphora pratensis resembles several taxa in the Halamphora veneta (Kützing) Levkov (2009: 242 ; basionym: Amphora veneta Kützing 1844: 108 ) group, including, H. veneta , Halamphora veneta var. somalica (Frenguelli) Levkov (2009: 243 ; basionym: Amphora veneta var. somalica Frenguelli 1929: 403 ), Halamphora oligotraphenta (Lange-Bertalot) Levkov (2009: 213 ; basionym: Amphora oligotraphenta Lange-Bertalot 1996: 28 ), Halamphora coloradiana Stepanek & Kociolek (2013: 73) and Halamphora coraensis (Foged) Levkov (2009: 180 ; basionym: Amphora coraensis Foged 1964: 123 ). Halamphora pratensis can be distinguished from H. veneta by its distinctly protracted and narrowly rounded valve ends, its finer striation ( Patrick and Reimer 1975, give 14–20 striae in 10 μm at center valve and 26 in 10 μm near the apices) and the more closely spaced proximal raphe ends. In the SEM, H. pratensis exhibits a less well defined marginal ridge than is seen in H. veneta . Halamphora pratensis shares protracted valve ends with H. veneta var. somalica , H. oligotraphenta and H. coloradiana . Halamphora pratensis can easily be distinguished from these taxa by its larger and comparably wider valves. Halamphora pratensis is quite similar to H. coraensis in valve dimensions and striae count ( Levkov 2009, gives length 26–36 μm, breadth 4.5–6.5 μm and a dorsal striae count of 24–26 in 10μm). Unlike H. pratensis , H. coraensis exhibits distinctly capitate valve ends ( Levkov 2009: pl. 107, Figs 33–37 ) and is found in freshwater oligotrophic waters of northern Europe. Halamphora pratensis also shares similar valve dimensions and striae counts with the punctate taxon Halamphora ausloosiana Van de Vijver & Kopalová (2014: 379) ( Van de Vijver et al. 2014 give length 22–34, breadth 4.0–6.5, and 22–28 dorsal striae in 10 μm for this taxon) recently described from an Antarctic Island. In the LM H. ausloosiana can be distinguished from H. pratensis by its sub-capitate valve ends and lack of more widely spaced dorsal central striae. In the SEM H. ausloosiana exhibits a broad dorsal raphe ledge and biseriate dorsal striae, both absent in H. pratensis .

Figures

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

FIGURES 10–14: SEM Halamphora pratensis sp. nov. Fig. 10. External whole valve view. Fig. 11. Internal whole valve view. Fig. 12. Detail of valve apex showing marginal ridge wrapping around distal raphe end to the ventral margin (arrow). Fig. 13. Detail of internal valve center showing thickened central virgae (arrow). Fig. 14. Whole frustule in dorsal girdle view showing girdle bands with two rows of poroids. Scale bars = 1 μm.

FIGURES 29–39: LM. Halamphora attenuata sp. nov. Single valves showing size range. Fig. 31. Holotype specimen. Scale bar = 10 μm.