Nitzschia shanxiensis Q. Liu & S.L. Xie, 2017

Liu, Qi, Wu, Weiwei, Wang, Jie, Feng, Jia, Lv, Junping, Kociolek, John Patrick & Xie, Shulian, 2017, Valve ultrastructure of Nitzschia shanxiensis nom. nov., stat. nov. and N. tabellaria (Bacillariales, Bacillariophyceae), with comments on their systematic position, Phytotaxa 312 (2), pp. 228-236 : 229-230

Nitzschia shanxiensis Q. Liu & S.L. Xie nom. nov., stat. nov.

( Figs 1–12 , 25–30 )

Basionym: Nitzschia sinuata var. constricta Chen & Zhu 1989 . New Species and arieties of the Diatoms from Suoxiyu, Hunan, China, in Zhu & Chen (1989a), The algal flora and aquatic fauna of the Wulingyuan Nature Reserve Area, Hunan, China, p. 36, fig. I: 8.

The name was presented in the text by Chen and Zhu (1989) as “ Nitzschia sinuata var. constriata ”, but in the figure legend it was listed as N. sinuata var. constricta . Based on the description, we consider the name in the text as a typographic error.

To be recognized as a separate species, this diatom requires a new name, since Nitzschia constricta is occupied with both Nitzschia constricta (Kützing) Ralfs in Pritchard (1861) (Basionym: Synedra constricta ( Kützing 1844: 64)) , and the later homonym Nitzschia constricta (Gregory) Grunow in Cleve & Grunow 1880 (Basionym: Tryblionella constricta ( Gregory 1855: 40)) .

Frustules solitary. Valves broadly lanceolate with constricted margins and protracted, round apices. Constriction slightly more pronounced on one side. Raphe eccentric, on a wide, low canal. Fibulae elongated and occupy about one-half the valve surface, somewhat irregularly distributed along the keel, numbering 5–7 in 10 μm. Valve length 16.5–19.0 μm, breadth 5.0–6.0 μm (n=20). Uniseriate striae distinctly punctate, parallel around the center to nearly radiate towards the ends, often 3–4 striae between two fibulae, 22–23 in 10 μm. Fibulate raphe system occurs on opposite sides of frustule.

Distribution and ecology:— Shanxi province, Niangziguan spring basin, China, pH 8.2, temperature 17°C; also collected in Lake Pingyang, attached to a large stone. Zhangbu Geology Park, Guizhou province

Observations:— In SEM, valves are broad, with a distinct constricted center and tapering narrowly to rounded apices ( Fig. 25 ). Externally, striae are composed of individual, circular to elongate areolae with small occlusions ( Fig. 26 ). The keel is a simple ridge extending marginally from apex to apex ( Fig. 25 ). The raphe is filiform and without proximal raphe ends ( Figs 25, 26 ). The distal raphe ends hooked towards the same side of the valve ( Figs 25, 27 ).

Internally, the areolae are rounded to elongate pores ( Fig. 28 ). The canal raphe is subtended by fibulae extending about one-half the valve surface ( Figs 28, 29 ). Narrow fibulae connect to the valve face internally with a wider base, sometimes with two or three smaller sections. Fibulae also attached to the base of the valve mantle. The canal raphe has a series of elliptical portulae ( Figs 29, 30 ). The distal raphe ends terminate as helictoglossae and are positioned on the mantle at the apices ( Figs 28, 30 ).

Discussion related to Nitzschia shanxiensis : There are several species to which this taxon should be compared. These species, considered by Lange-Bertalot (1980) to be conspecific, are in our opinion divided into two groups. The first group includes several fossils described from France, such as Grunowia moissacensis ( Heribaud 1903: 33) . This diatom is, comparatively large (40 μm in length, 6 μm wide) and has 5.5–6.0 fibulae in 10 μm ( Table 1). Striae of G. moissacensis number 20 in 10 μm and the valve tapers gently to the apices. Nitzschia denticula var. delognei (Grunow in Van Heurck 1881: 176; = N. sinuata var. delognei (Grunow in Van Heurck) Lange-Bertalot), described as extant from the Botanical Garden in Brussels, Belgium, is much smaller (10–20 μm long, 3–4 μm wide) and more finely ornamented, with 6–8 fibulae per 10 μm and 22–26 striae per 10 μm ( Lange-Bertalot 1980; see figs 83, 84). Nitzschia sinuata var. denticuloides (Biswas 1964: 511) may also belong to this group. Its morphometry in terms of size (length 10–22 μm, breadth 3–4 μm) and density of ornamentation (fibulae 6–8 in 10 μm; striae 22–32 in 10 μm) suggest a close relationship with Grunow’s taxon. N. sinuata var. denticuloides was described from northern Wales. These taxa are more lanceolate in shape, and lack the undulate margins of N. sinuata and inflated center of N. tabellaria .

A second section of this first group of species was described as extant from Asia. These include N. heidenii (Meister) Hustedt , first described from Japan ( Meister 1914: 229) and later reported by Hustedt (in Schmidt 1924, plate 351, figs 9-13) from that country. This diatom was originally described by Meister as being relatively large (28–40 μm long, 7–8 μm wide) and more coarsely ornamented with 5–6 fibulae in 10 μm and 18–20 striae in 10 μm. Lange- Bertalot’s illustrations (1980, figs 77, 78) show large valves tapering gently to small capitate apices. Varieties of this species were described from elsewhere in Asia, including N. heidenii var. baicalensis ( Skvortzow & Meyer 1928: 39) from Lake Baikal and N. heidenii var. lanceolata (Kobayashi 1960: 76) and N. heidenii var. minor (Kobayashi 1960: 76) from Japan. Peterson described N. heidenii var. pamirensis (Peterson 1939: 52) from Central Asia, and this taxon was reported by Foged (1959) from Afghanistan.While Peterson’s taxon has protracted apices similar to N. shanxiensis , it is much more narrow (3.5–4.2 μm for N. heidenii var. pamirensis versus 5–6 μm wide in N. shanxiensis ), with finer fibulae (6.0– 6.5 in 10 μm versus 5–7 in 10 μm) and striae (27 in 10 μm versus 22–23 in 10 μm). These Asian species, like the fossil extant taxa from Europe, have lanceolate outlines and lack the undulate outlines of N. sinuata and inflation found in N. tabellaria .

The second group of species includes those with undulate margins, and is comprised of N. sinuata and N. tabellaria . We include observations of the latter species from China for comparison.

Figures

FIGURES 1–24. LM micrographs of Nitzschia shanxiensis and Nitzschia tabellaria. 1–12: Nitzschia shanxiensis. 13–24: Nitzschia tabellaria. Scale bar: 10 μm.

FIGURES 25–30. SEM micrographs of Nitzschia shanxiensis. 25. External view of the valve, showing the keel extending marginally from apex to apex. 26. Central area showing the raphe is without central raphe ending, areolae are circular to elongate. 27. Valve terminus showing the hooked raphe ends. 28. Internal view of the valve, showing the canal raphe subtended by fibulae. 29. Internal view of valve center showing the fibulae structures. 30. Distal raphe ends showing helictoglossae and are positioned on the mantle at the apices.