Hippodonta qinghainensis Peng & Rioual, 2014

Peng, Yumei, Rioual, Patrick, Levkov, Zlatko, Williams, David M. & Jin, Zhangdong, 2014, Morphology and ultrastructure of Hippodonta qinghainensis sp. nov. (Bacillariophyceae), a new diatom from Lake Qinghai, China, Phytotaxa 186 (2), pp. 61-74 : 65

Hippodonta qinghainensis Peng & Rioual sp. nov. ( Figs 3–37 )

Type:– CHINA. Qinghai Province, Qinghai Lake, 3194 m, 36°48’39.1’’N, 100°8’12.0’’E, sediment trap sample, 10 m water depth, collected by Mrs Yumei Peng, Institute of Earth Environment, Chinese Academy of Sciences , Xi’an (holotype slide IGGDC-Qtrap- 20111105!, holotype specimen illustrated in Fig 11 , located using England Finder H 16/4); BM 101 710 (isotype slide) .

LM ( Figs 3–27 ): Frustules rectangular with weakly concave central nodule in girdle view. Cells solitary, valves elliptic-lanceolate to rhombic-lanceolate with obtusely rounded ends, not protracted. Valve length 16–50 µm, width 5–8 µm. Axial area narrow and linear, weakly expanding into a small rectangular to panduriform central area, defined by two shortened central striae. Terminal areas clearly distinguishable in LM, lunate to semicircular and cap-like. Raphe filiform, moderately pronounced, with simple linear or teardrop-shaped central endings, weakly deflected at the terminal ends. Striae coarse, 8–11 in 10 µm, moderately radiate in the middle, becoming parallel to convergent near valve ends. Interstriae of equal or narrower width than striae near the valve apices, becoming wider than striae in the middle of valve. Lineolae composing the striae densely spaced within each, not discernible in LM.

SEM ( Figs 28–37 ): Externally, valve face gently curved in transapical section merging gradually into mantle. Raphe slits quite fine.Terminal pores of raphe distant, weakly advancing into terminal area, deflected towards secondary side of valve (i.e. where the Voigt discordances are present). Central raphe endings small, forming teardrop-shaped depressions and slightly bent towards same side with terminal end. Striae uniseriate throughout valve face and mantle. Central row of lineolae present on valve mantle only. Lineolae linear, 38–51 in 10 µm. Two rows of apical areolae surround the valve apex, positioned on apical valve mantle. Prominent hyaline area present throughout valve mantle. Girdle band quite broad and unornamented. Internally, striae positioned in shallow linear depressions. Central raphe endings simple, linear, gradually disappearing. Semicircular hyaline area clearly developed in central area. Linear raphe slits distally terminated with weak, crescent-shaped helictoglossae, positioned just before terminal area and in line with raphe slits. Terminal area internally quite prominent, boomerang-shape.

Observations:— As the valves are arched and the girdle relatively broad, they often lie in girdle view or at an angle in valve view.

Results of statistical analyses: Boxplots of the conventional morphometric variables valve length, width and stria density show considerable overlap between the six species of Hippodonta investigated ( Figs 38–40 ). Nevertheless, the classification tree model based on these three variables ( Fig 41 ) performs reasonably well in separating the six species with a misclassification error rate of 10.4% (11/106).

The CVA based on geometric variables was highly significant (Wilk’s lambda = 0.0007, p <0.0001) and the first two axes, representing 85.6% of the variation, clearly separated the different species of Hippodonta ( Fig 42 ). Pairwise MANOVA comparisons show that the shape of H. qinghainensis was clearly different of that of H. hungarica , H. intermedia and H. costuloides as indicated by Bonferroni-corrected Hotelling’s p- values <0.001. However, the shape difference between H. qinghainensis and H. conspicua and H. neglecta was not significant ( Table 2). The misclassification error rate of the CVA on geometric variables is ~17% (18/106). For H. qinghainensis in particular, the error rate is 14% (7/50) as shown in the confusion matrix ( Table 2).

Etymology:— The species epithet refers to Lake Qinghai.

Distribution and ecology:— Lake Qinghai is a brackish and alkaline lake with high pH ( Table 1). Apart from the trap samples, H. qinghainensis was found only in one out of five sampling sites and at very low abundance. It was found on filamentous green algae but not in the epilithon and epipsammon samples taken near the shore. In the trap samples, H. qinghainensis was found commonly but never in high abundance (maximum abundance = 1.2%). No seasonal trends could be deduced from its pattern of occurrence.

Figures

FIGURE 41. Classification tree model, fitted using binary recursive partitioning, that shows splits used to separate the six species of Hippodonta on the basis of the three conventional variables: valve length, valve width and stria density.

FIGURE 42. Ordination plots representing the first two axes of the Canonical Variates Analysis (CVA) performed on the normalized coordinates of the morphological landmarks digitized on LM images of Hippodonta qinghainensis and other species of Hippodonta.

FIGURES 3–27. LM images of Hippodonta qinghainensis. Scale bar = 10 µm.

FIGURES 28–33. SEM images of Hippodonta qinghainensis. Fig. 28. External view of entire valve. Striae composed of simple lineolae throughout. Figs 29, 31. Close-up of apices. Terminal pores of raphe are weakly deflected towards one valve side. Two rows of apical areolae at the valve apices.Fig.30.Close-up of central area.External central raphe endingsweakly developed, teardrop-shapeddepressions. Fig. 32. External view of complete frustules showing broad, unornamented girdle. Fig. 33. Detail of one apex in girdle view, showing two rows of apical areolae. Scale bars in Figs 28, 32, 33 = 2 µm; Figs 29, 30, 31 = 1 µm.

FIGURES 34–37. SEM images of Hippodonta qinghainensis. Figs 34, 35. Internal view of entire valves of different size. Striae composed of simple lineolae, positioned in quite shallow and narrow depressions; interstriae strongly pronounced. Some lineolae are still covered by volae. Raphe-sternum thickened towards central raphe endings. Fig. 36. Internal view, detail of apex. Linear raphe slit distally terminated by crescent-shaped helictoglossa, positioned just below terminal area. Fig. 37. Internal, oblique view showing two rows of lineolae around the valve apex. Scale bars in Fig. 34 = 3 µm; Fig. 35, 37 = 2 µm; Fig. 36 = 1 µm.

FIGURES 38–40. Boxplots showing quantile distributions of valves characters for Hippodonta qinghainensis 38. Valve length. 39. Valve width. 40. Stria density (= number of striae in 10 µm). The 25–75 percent quartiles (excluding outliers) are drawn using a box. The median is shown with a horizontal line inside the box. The whiskers represent the upper and lower “inner fence”, i.e. are drawn from the edge of the box up to the largest/lowest data point less than 1.5 times the box height. Outliers, i.e. values outside the inner fences, are shown as circles if they lie further from the edge of the box than 3 times the box height.