Gyrosigma peisonis var. major Peng, Rioual & Sterrenburg, 2016

Peng, Yumei, Rioual, Patrick, Jin, Zhangdong & Sterrenburg, Frithjof A. S., 2016, Gyrosigma peisonis var. major var. nov., a new variety of Gyrosigma peisonis (Bacillariophyta) from Lake Qinghai, China, Phytotaxa 245 (2), pp. 119-128 : 122-124

Gyrosigma peisonis var. major Peng, Rioual & Sterrenburg , var. nov. ( Figs 4–18 )

LM observations ( Figs 4–9 ): valve slightly sigmoid, linear to lanceolate, gradually tapering to bluntly rounded ends. Valve length 130–192 μm, width 12.0–16.3 μm. Middle of the valve face appears flat (on about half the valve width), becoming clearly vaulting in the transapical axis towards the edges. Vaulting is similar between the centre and terminal portions of the valve. Axial area wide and sigmoid, with a longitudinally oval central area. Terminal areas small, hardly visible in LM. Raphe slight to moderate double curvature, distal ends slightly eccentric toward each convex side. Striae fine and parallel, except central part deformed according to the oval central area. Longitudinal striae 23–27 in 10 μm, transverse striae 20–24 in 10 μm, longitudinal/transverse density ratio 0.8 to 1.0 (median value ca. 0.9). SEM observations ( Figs 10–18 ): externally, valve face gently curved in transapical section. Raphe slits quite fine, proximal raphe ends abruptly-deflected, crooked oppositely in the central area ( Figs 10, 11 ), terminal raphe ends deflected to the opposite side of proximal ends ( Figs 12, 13 ). Terminal areas, represented by non-areolated fields, funnel-shaped, unilaterally dilated to the concave side of the valve, in semi-lateral position, with a row of apical lineolae surrounding the valve apex ( Figs 12, 13 ). These apical areolae are located at the junction between the valve face and the mantle ( Fig. 12 ). Striae composed of slit-like lineolae, aligned into longitudinal lines, while the lineolae on the valve face margin are arranged splayed ( Fig. 10 ). Internally, raphe slits fine, with thickened and narrow sterna ( Fig. 14 ). Central raphe endings T-shaped, positioned at the polar end of the elliptical central area ( Figs 15, 16 ). The distal raphe terminated in raised and thickened helictoglossa ( Figs 17, 18 ). Striae composed of round to elliptical areolae.

Type:— CHINA. Qinghai Province: Qinghai Lake, 36° 48’ 39.1” N, 100° 8’ 12.0” E, 3194 m a.s.l., sediment trap sample, 10 m water depth, Y. Peng, 31 May 2014 (holotype: IGGDC!, individual in slide Qtrap-20140531, illustrated in Fig. 4 , located using England Finder K13/1 or at coordinates 42.5 and 14.5. Isotype: BM!, slide 101/812, Natural History Museum, London, United Kingdom).

Etymology:—The varietal epithet refers to the large cell size of this taxon.

Figures

FIGURES 4–9. LM images of Gyrosigma peisonis var. major. Scale bar = 20 μm.

FIGURES 10–18. SEM images of Gyrosigma peisonis var. major. 10, 11. External view, close-up on central area. 12, 13. External view, close-up on apices. 14. Internal view of entire valve. 15, 16. Internal view, close-up on central area. 17, 18. Internal view, close-up on apices. Scale bars in Figs 10–13 and 15–18 = 1 μm, Fig. 14 = 10 μm.