Nitzschia gaoi 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 : 266-268

Nitzschia gaoi Bing Liu, S. Blanco et B.Q. Huang , sp. nov. ( Figs 23–49 )

Synonym: Nitzschia sp. “(?) Als Nitzschia lorenziana in Cleve & Möller 209, Rovigno/Adria, evtl. Nitzschia behrei zuzuordnen” in Krammer & Lange-Bertalot (1988: fig 86, 5)

Valves dorsiventral, with long produced rostrate apices, 83–107 μm long, 3.8–5.7 μm broad. Canal raphe prominent and slightly eccentric or positioned along the central axis of the valve. Fibulae distinct, irregularly spaced, 8–11 in 10 μm in the middle, 8–13 in 10 μm at apices. Two conopea are present and recognizable as two parallel lines on either side of the raphe.

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 20154G (holotype JIU! G201504, illustrated in Fig. 24 , 2.2 mm south by 9.9 mm east from the benchmark cross on the slide; isotype CL! 201304, illustrated in Fig. 29 , 5.5 mm south by 4.0 mm east from the benchmark cross on the slide) .

Description: —LM: Valves dorsiventral, with a ventral margin straight in the middle but concave to almost straight at apices, which are long produced, rostrate, and an arched and convex dorsal margin ( Figs 23–29 ), 83–107 μm long, 3.8–5.7 μm broad (N=30). The two long produced apices are slightly arched toward the ventral side ( Figs 24, 26, 28 ), or only one apex arched and the other straight ( Figs 23, 25, 27, 29 ). Canal raphe prominent and slightly eccentric ( Figs 23–25, 27–29 ), or positioned along the central axis of the valve ( Fig. 26 ). Fibulae distinct, irregularly spaced, parallel to the transapical axis, 8–11 in 10 μm in the middle, 8–13 in 10 μm at apices. Interspaces of the fibulae rectangular or round. Two conopea are present and recognizable as two parallel lines on either side of the raphe ( Figs 23–29 ). Transapical striae are not visible with light microscopy.

SEM: External views: Valve dorsiventral with long produced, rostrate apices arched towards the ventral side, raphe system present on both sides of the valves (nitzschioid symmetry, Figs 30–31 ). Conopea distinctive from pole to pole, constant in width ( Figs 30–33 ). At the poles, the conopeum is fused to the valve face and apical pore fields are present ( Figs 34–35 ). Transapical costae conspicuous in intact valves, 40 in 10 μm, connected through few short siliceous structures ( Fig. 36 ). Some spines extend from the conopea, fusing into certain transapical costae ( Fig. 36 , arrowheads). Two small conopea flaps, which cover the areolae, occur on each side of each transapical costa ( Figs 36–39 ), but not distinctive in eroded individuals ( Figs 37–38 ). Striae uniseriate, 40 in 10 μm, formed by round poroids, 50 in 10 μm. Raphe lacking central raphe endings, terminal fissures hooked towards the dorsal side ( Figs 34–38 ). A conopeal canal is present ( Fig. 37 , double-head arrows, Fig. 39 , cc).

Internal views: One apex bending toward the ventral side and the other almost straight ( Figs 40–42 ). Raphe running continuously from pole to pole and subtended by bar-like fibulae ( Figs 40–43 ). Towards the poles the interspaces between the fibulae very slightly narrower transapically than near the centre of the valve ( Fig. 40 ). Raphe always rising on a keel and the subtended zones markedly different from the uncovered zones ( Fig. 43 ). The zone of valve face subtended by the conopeum has no areolae in most part but these are present near or on the wall of raphe canal ( Fig. 43 , cv, arrow). The distinctive apical pore field present ( Fig. 44 , arrow).

Girdle band views: One girdle band open at one apex and close at another apex ( Figs 45–47 ). One transverse row of areolae existing in this girdle band ( Figs 46–48 ) and the areolae covered by hymenes and terminating near each apex ( Figs 46, 49 , arrows).

Etymology: —Named after Professor Yahui Gao of Xiamen University, China, in recognition of his contributions to the study of diatoms.

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: —Taking into account the valve outline, N. gaoi resembles N. behrei Husted (1959: 99) , N. bartholomei Grunow (in Cleve and Grunow 1880: 102), and a N. spp. described in Krammer & Lange-Bertalot (1988: 126, fig. 86: 5). However the valve of N. behrei is much longer (220–250 μm vs 83–107 μm), and the stria dense of N. bartholomei is much lower (13.5 in 10 μm vs 40 in 10 μm). Moreover, N. behrei and N. bartholomei both do not possess conopeum. The raphe system in N. williamsii Alakananda, P.B.Hamilton & Karthick in Alakananda et al. (2012: 19) is completely eccentric and its apices are not long produced. Nitzschia gaoi is very probably conspecific with the “ Nitschia species ” described in Krammer & Lange-Bertalot (1988: 126, fig. 86: 5) which was tentatively assigned to N. behrei or N. lorenziana Grunow in Cleve & Möller (1879: 208).

Figures

FIGURES 23–29. Nitzschia gaoi, sp. nov., LM. 23–25. Three valves showing a slightly eccentric raphe system. 24. Photograph of holotype. 26. One valve showing a centrally positioned raphe system. 27–29. Three valves showing a slightly eccentric raphe system. 27. Photograph of isotype specimen. Scale bar = 10 μm for all figures.

FIGURES 30–39. Nitzschia gaoi, sp. nov., external views, SEM. 30–31. Two complete valves, note the nitzschioid symmetry of the raphe system. 32–33. Apices, note the constant width of the conopeum. 34–35. Apices showing the apical pore fields and the hooked terminal fissures towards the dorsal side. 36. Intact central area, showing costae, conopea, and the fusing of costae with conopeal spines (arrowheads). 37. Eroded area showing small conopea occuring on each side of each costa, and a transverse row of areolae appearing in a girdle band. 38. Eroded area showing striae and areolae. 39. Broken central area, showing the canal-raphe-conopeum system (cc = conopeal canal). Scale bars = 10 μm (Figs 30–31), 1 μm (Figs 32–39).

FIGURES 40–44. Nitzschia gaoi, sp. nov., internal views, SEM. 40. A whole valve, note the upper apex very slightly arched toward the ventral side. 41–42. Apices, note one apex bending toward the ventral side (Fig. 41, two arrows) and the other almost straight (Fig. 42, two arrows). 43. Central area, note that the zone of valve face subtended by the conopeum (cv) has no areolae in most part but these are present near or on the wall of raphe canal (arrow). 44. Detail of the apex, note the distinctive apical pore field (arrow). Scale bars = 10 μm (Fig. 40), 1 μm (Figs 41–44).

FIGURES 45–49. Nitzschia gaoi, sp. nov., girdle band views, SEM. 45. Internal view of a whole valve with one girdle band. 46–47. Apices, note that the girdle band is open at one apex (Fig. 46) but closed at the other (Fig. 47). 48. External view of the apex, note the girdle band (arrow). 49. Apex showing the areolae of the girdle band covered by hymenes and terminating near each apex (Figs 46, 49, arrows). Scale bars = 10 μm (Fig. 45), 1 μm (Figs 46–49).

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.