Sichuaniella deqinensis, Li, 2020

Wu, Han, Zhang, Teng-Zhong, Li, Yan-Ling, Metzeltin, Ditmar, Lange-Bertalot, Horst & Kociolek, John Patrick, 2020, Sichuaniella deqinensis sp. nov., a new diatom species (Bacillariophyceae) from a high altitude lake in the Hengduan Mountains, SW China, Phytotaxa 449 (1), pp. 83-89 : 84-85

Sichuaniella deqinensis nov. sp. Li Figs. 1–59.

Description: LM: Frustules biraphid. Girdle views retangular, often forming short chains (Figs 24–27). Girdle views can be observed in the accumulations of silicate. Valves broadly elliptical with broadly rounded, not protracted ends. Length 11–20 µm, breadth 5.5–7.9 µm. Raphe branches appear somewhat diffuse lying in a lanceolate axial area. Central area elliptic, about 1/2 the width of the valve. Central pores on the valve outside (focus) conspicuously widely spaced. Below the surface, slightly displaced distally from the central raphe ends, appear two dark spots. Transapical striae are very coarse, 7–8 in 10 µm. Striae rather strongly radiate becoming more radiate towards the valve ends. Areolae are not discernible in LM view.

SEM: external view (Figs 36–45: Valve faces (fronts) strongly domed, continual transition to the mantle. Raphe slits noticeably broad with short terminal fissures deflected to the secondary side (sometime indistinct) running into a small circular groove (Figs. 42–45). Central ends of the raphe curve to the primary side into very large, crater-like grooves (Fig. 39). Transapical striae consist of three to mostly four series of circular open areola foramina separated by broad interstriae. A group of pores can be seen at each apex, and they appear physically undifferentiated from the areolae (Figs. 41–44). Areolar density is 40–50 in 10 µm. Spines or differentiated apical pore fields lacking. The girdle consists of one or two narrower, unperforated copulae (Fig. 37). Internal SEM view (Figs. 46–56): Transapical costae form a rather high relief between the alveoli. At the apices, the pores there appear occluded, similar to what is seen in apical pore fields in freshwater gomphonemoid diatoms and apical pore field-bearing cymbelloid diatoms. The central raphe ends are masked by a silica flap, no intermissio visible. Two elliptic cavities below the flaps are connected with narrow canals in the two peculiar appendices which protrude “pervalvar” into the valve interior. These appendices have a spongeous consistency lying on the primary valve side and make the valve interior asymmetrical consequently.

Type:— CHINA. Yunnan Province: Xianggelila City, Gaoligong Mountain, Lake Deqin5 , 28°30’15.75’’ N, 98°59’26.58’’E, elevation 4734 m a.s.l., samples collected by Dr. Yulan, Luo, 14 October 2017. Holotype Deqin5- 1 in Coll. Li Yanling, Yunnan University., Kunming, China. Figure 1 is of the holotype.

Etymology:—The specific epithet ‘deqinensis’ refers to the locality from which the new species was described.

Ecology

Sichuaniella deqinensis is known only from Lake Deqin5, a high-altitude freshwater lake situated at 4734 m a.s.l. with slightly alkaline pH (8.22), conductivity (125μS/cm) and high water transparency (Secchi depth) 7. 2 m. In Lake Deqin5, at depth of 12.7 m, this species was associated with Achnanthidium minutissimum (Kützing) Czarnecki ( Czarnecki 1994: 157) (27.6%), Staurosira venter (Ehrenberg) Cleve & Möller (1877: 242) (29.7%), Staurosira construens Grunow (1843: 424) (4.4%), Encyonema minutum (Hilse) Mann ( Round et al. 1990: 167) (2.7%), and several at present unidentified species of Fragilaria , Nitzschia and Cymbella .