Navicula amoyensis Gao, Sun & Chen, 2017

Chen, Changping, Sun, Jiandong, Zhao, Long, Sun, Lin, Li, Xuesong, Liang, Junrong & Gao, Yahui, 2017, Navicula amoyensis sp. nov. (Bacillariophyceae), a new benthic brackish diatom species from the Jiulong River estuary, Southern China, Phytotaxa 291 (4), pp. 253-263 : 254-256

Navicula amoyensis Gao, Sun & Chen , sp. nov. ( Figs 1–22)

LM ( Figs 1–8): Frustules rectangular in girdle view and somewhat constricted in the middle ( Fig. 8). Cells solitary, valves linear-lanceolate to elliptic-lanceolate with rounded apices, not protracted. Valve length 38–67 μm, width 8–10 μm, the ratio of length to width is 3.8–5. Raphe filiform, moderately pronounced, with simple linear central endings, weakly deflected at the terminal ends. Axial area narrow and linear, expanding into asymmetrical rectangular to panduriform central nodule, defined by several shortened central striae ( Figs 1–7). Terminal area distinguishable in LM, moderately large, semi-circular or triangular in shape. Striae coarse, strongly radiate in the middle, more or less parallel to very weakly convergent near valve ends. Striae rarely observed to be nearly parallel at middle of valve. Striae evenly spaced throughout, 8–9 in 10 μm. Interstriae of broader or equal width than striae. Lineolae composing the striae densely spaced, not discernible in LM ( Figs 1–7).

SEM ( Figs 9–22 ): External views: valve face gently curved in transapical section merging gradually into mantle. Raphe filiform, the axial area is not elevated over valve surface externally ( Fig. 9 ). Central raphe endings continuous ( Fig. 10 ). Terminal raphe endings distant, hooked towards the secondary side of the valve ( Figs 11, 12 ). Striae uniseriate throughout valve face and mantle. 4 or 6 rows of central lineolae present on valve mantle only. Lineolae linear or slitlike, 36–39 in 10 μm ( Figs 9–12 ). Two rows of apical areolae surround the valve apex, positioned on apical valve mantle. The number and length in two rows of apical areolae are different. Prominent hyaline area present throughout valve mantle in girdle view. Girdle band quite broad and unornamented, with pectinate margin ( Figs 21, 22 ).

Internal views: Striae positioned in shallow linear depressions ( Fig. 17 ). Central raphe endings are simple, linear, with a distinct central interruption ( Fig. 15 ). An accessory rib, lies at the primary side of the raphe-sternum, with an additional lateral thickening at the center of the accessory rib ( Figs 13, 14 ). Semicircular hyaline area clearly developed in central area ( Figs 18–20 ). Terminal raphe fissures end in rounded helictoglossae, and in line with the raphe fissures. The thickened area behind the helictoglossae is narrow and transverse ( Figs 16 , 19, 20 ).

Type:— China. The intertidal zone of sand beach in Nantaiwu district, the estuary of Jiulong River, the southwest Xiamen island, Fujian (24°22′55″N, 118°3′46″E), 15 th December 2015, collector J. Sun, School of Life Sciences, Xiamen University, Xiamen (holotype XMU!, individual on slide MMDL 151201, here illustrated as fig 5. Isotype XMU!, slide MMDL 151202).

Etymology:—The specific epithet refers to Xiamen which is close to the sampling site (the Latin adjective of Xiamen is amoyensis ).

Ecology:—In the sampling site, the sediment type is classed as medium silt, salinity of water is 25.3 ± 3.6 ppt, pH is 7.96 ± 0.56, and water temperature is 25.7 ± 3.4 °C showing that N. amoyensis is epipelic and lives in the coastal environment. The motile cells were observed within the sediments. In living cells the central portion is accentuated by the two plastids, which lie against each side of the girdle. Each plastid contains a rod-shaped pyrenoid. In girdle view the plastids occupy more than half the length of the cell. Together with N. amoyensis the most frequent species in the assemblage were: Halamphora coffeaeformis (C. Agardh) Levkov , Nitzschia lorenziana Grunow , Cocconeis scutellum var. parva (Grunow) Cleve and Navicula cryptocephala Kützing.

Observations: — Navicula amoyensis can be compared to Navicula cari Ehrenberg (1986:96) , Navicula libonensis Schoemann (1986: 99) , Navicula veneta Kutzing ( Cox 1995: 98), Navicula cincta (Ehrenberg) Ralfs ( Witkowski 2000: 662) and Navicula lundii Reichardt (Langer-Bertalot 2001: 46) ( Table 1). N. veneta and N. cincta differ from N. amoyensis mainly by their central area and hooked terminal raphe endings. N. libonensis is smaller (25–40 μm length, 5.5–8 μm width), with lower density of areolae. N. lundii differs from N. amoyensis by its narrower valves, smaller central area and higher density of striae. N. cari is most similar to N. amoyensis , but is distinguished from it by its striae pattern (9–12 striae in 10 μm, paralle to convergent at the ends) and hooked terminal raphe endings ( Table 1). The following features in our SEM observations distinguish Navicula amoyensis from these species, a) terminal raphe endings, b) central area, c) terminal area, d) apical pores, and e) internal accessory ribs ( Figs 1–22).

Figures

FIGURES 9–12. Fig. 9. External view of entire valve with terminal areas (arrow). Fig. 10. Central area showing the distinct continuous external central raphe endings. Figs 11, 12. Valve apices showing the external terminal raphe fissures deflected towards on the secondary valve side (arrow). Two rows of apical areolae at the valve apices. Scale bars in fig. 9 = 10 μm; fig. 10 = 2 μm; figs 11, 12 = 1 μm.

FIGURES 13–18. SEM micrographs of Navicula amoyensis sp. nov. Figs 13, 14. Internal views of entire valves of different frustules, showing an additional lateral thickening at the centre of the accessory rib (arrow). Fig. 15. Internal valve view showing details of central raphe fissures with a distinct central interruption (arrow). Fig. 16. Internal view showing details of the valve apices, where linear raphe axis distally terminated by more or less rounded helictoglossa (arrow) and positioned just below the terminal area. Fig. 17. Internal view. Striae composed of simple slit-like lineolae, positioned in shallow and narrow depressions (arrow). Fig. 18. Internal central raphe endings, interrupted by an extended thickening accessory rib (arrow). Scale bars in figs 13, 14 = 5 μm; fig. 15 = 2μm; figs 16–18 = 1 μm.

FIGURES 19–22. SEM micrographs of internal and girdle views of Navicula amoyensis under SEM. Figs 19, 20. Internal view of entire valves of different frustules. Note that the helictoglossa is almost central (arrow). Figs 21, 22. Girdle views showing the constricted frustules in the middle. External view of frustules showing broad girdle with pectinate margin (arrow). Scale bars in figs 19–22 = 10 μm.