Nitzschia arierae Bing Liu, S. Blanco et B.Q. Huang, 2015

Liu, Bing, Blanco, Saúl & Huang, Bangqin, 2015, Two new Nitzschia species (Bacillariophyceae) from China, possessing a canal-raphe-conopeum system, Phytotaxa 231 (3), pp. 260-270 : 261-266

Nitzschia arierae Bing Liu, S. Blanco et B.Q. Huang , sp. nov. ( Figs 1–22 )

Valves dorsiventral, 54–156 μm long, 6.5–10.9 μm broad. Canal raphe prominent, centrally positioned. Fibulae distinct, 5.0– 7.5 in 10 μm. Conopea present on either side of the raphe, recognizable as two parallel lines. Type : — China. Fujian: Xiamen Bay , Dadeng Island , the middle intertidal zone of Yangtang Village , 24°31′54″ N, 118°20′16″ E, 0 m a.s.l., 15 July 2013, Bing Liu 20153G (holotype JIU! G201503, illustrated in Fig. 3 , 8.9 mm south by 9.7 mm east from the benchmark cross on the slide; isotype CL! 201303, illustrated in Fig. 1 , 5.0 mm south by 15.6 mm east from the benchmark cross on the slide) .

Description: —LM: Valves dorsiventral, with a concave ventral margin, slightly tumid in the middle, and an arched and convex dorsal margin ( Figs 1–7 ), 54–156 μm long, 6.5–10.9 μm broad (N=30). Valve outline constant, but very variable in length, and less so in width ( Figs 1–7 ). Poles cuneate, ventrally bent. Striae not resolvable under LM. Canal raphe prominent, centrally positioned, lacking central raphe endings. Fibulae distinct and irregularly spaced, 5.0– 7.5 in 10 μm. Interspaces of the fibulae rectangular to square. Two conopea present on either side of the raphe, recognizable as two parallel lines. A row of dark spots, which supports the conopeum, are placed on the margin of each parallel line from pole to pole ( Fig. 1 , six arrows). At poles, helictoglossae distinctly marked as dark dots.

SEM: External views: Valve conopea extending out from the raphe canal on either side ( Figs 8–11 ). Conopea slightly arched, attached to both the raphe sternum and the wall of the raphe canal, strutted by two rows of supporting points and the margins of the conopea not completely fused to the valve ( Figs 8–11 ). Two rows of supporting points (appearing as dark spots in LM) irregularly spaced on both ventral and dorsal sides ( Figs 9–11 , arrows). Width of the conopeum constant except near each pole, where it becomes narrower ( Figs 9, 11 ). At poles, conopeum fused to the valve face and two large rectangular openings into the space beneath each conopeum ( Figs 9, 11 ). Apical pore field present ( Fig. 9 , wavy arrows). Striae uniseriate, 50–51 in 10 μm, formed by tiny round poroids. Raphe lacking central raphe endings; terminal fissures hooked towards the dorsal side (( Figs 9, 11 , arrowheads).

Internal views: Raphe running continuously from pole to pole and subtended by bar-like fibulae ( Figs 12–14 ). The interspaces between the fibulae become narrower transapically towards the poles than near the center of the valve ( Fig. 12 ). Raphe always rising on a keel ( Figs 13–14 ). Apical pore field distinctive and poroids in the keel zone present ( Fig. 13 , two arrows). The subtended zones markedly different from the uncovered zones ( Fig. 14 , double-head arrows). At the middle part of the dorsal side of the valve, one or two striae shortened ( Figs 14–16 , arrows) near a dichotomous stria ( Figs 14–16 , wavy arrows), and poroids in the raphe-sternum occur opposite to this dichotomous stria ( Figs 14–15 , arrowheads).

Canal-raphe-conopeum system: Raphe slit centrally positioned (e.g. Figs 17, 20 , r). Conopea themselves are not porous ( Figs 17–18 , c, rs). The supporting points are conspicuous ( Fig. 19 , arrows; Fig. 22 , sm). The uncovered zones in valve faces are different from the zones subtended by conopea, which are arched inwards and present areolae (e.g. Figs 18, 20–22 , v, cv). A keel (raphe canal wall) with areolae ( Fig. 21 , two arrows) supports both the conopeum and the raphe sternum ( Figs 18, 20–22 , k).

Etymology: —From the Latin noun ariera (banana), referring to the valve outline just like a banana.

Ecology: —In the sampling site of Yangtang Village, the sediment type (Wentworth scale) is classed as medium silt, salinity of water is 27 ± 1 ppt, pH is 7.98 ± 0.01, and water temperature is 28.1 ± 0.3 °C showing that N. arierae is epipelic and lives in the coastal environment.

Observations: — Mann & Trobajo (2014) described three new dorsiventral species in the subgenus Nitzschia . Although N. arierae and these three species all possess the canal-raphe-conopeum system and dorsiventral valve outline, the former differs from the latter by the centrally positioned canal raphe. Except above four species, no other dorsiventral Nitzschia taxa belonging to the subgenus Nitzschia can be found in the literature. The epithet of Nitzschia arcuata Gregory in Greville (1859: 82) recalls a dorsiventral valve outline, but N. arcuata is curved only in girdle view and does not possess conopeum. The small individuals of N. arierae are similar to those of N. bacillariaeformis Hustedt (1922: 149) , N. harderi Hustedt in Brendemühl (1949: 441), N. incrustans Grunow (1862: 566) or N. terricola Lund (1946: 100) , all of them showing straight frustules along the whole life cycle.

Figures

FIGURES 1–7. Nitzschia arierae, sp. nov., LM. 1–7. Seven valves showing size reduction. 1. Photograph of isotype specimen, note the two rows of dark spots (six arrows) and the two parallel lines on either side of the raphe. 3. Photograph of holotype, note the centrally positioned raphe system. Scale bar = 10 μm for all figures.

FIGURES 8–11. Nitzschia arierae, sp. nov., external views, SEM. 8. A whole valve, note the constant width of conopeum. 9. Apex, showing the apical pore field (wavy arrows), the hooked terminal fissure towards the dorsal side (arrowhead), and the supporting points (arrows). 10. Central area, note the supporting points (arrows). 11. Another apex, note the hooked terminal fissure towards the dorsal side (arrowhead) and the supporting points (arrows). Scale bars = 10 μm (Fig. 8), 1 μm (Figs 9–11).

FIGURES 12–16. Nitzschia arierae, sp. nov., internal views, SEM. 12. A whole valve, note the interspaces narrower towards the poles. 13. Apex, note the distinctive apical pore field and the poroids in the keel zone (two arrows). 14–16. Central areas, showing the subtended zone different from the uncovered zone (Fig. 14, double-head arrows), shortened striae (arrows), dichotomous striae (wavy arrows), and poroids present in the keel zone (Figs 14–15, arrowheads). Scale bars = 10 μm (Fig. 12), 1 μm (Figs 13–16).

FIGURES 17–22. Nitzschia arierae, sp. nov., canal-raphe-conopeum system, SEM. 17. External view of the apex, note that the conopea are fused into the valve (arrow). 18–19. External view of central area, note conopeal canal, raphe canal and supporting points. 20–22. Internal views, note keels and supporting marks. Abbreviations: c = conopeum, cc = conopeal canal, cv = zone of valve face subtended by conopeum, f = fibula, k = keel, r = raphe slit, rc = raphe canal, sm = supporting mark, v = uncovered zone of valve face. Scale bars = 1 μm (Figs 17–18, 20–22), 2 μm (Fig. 19).