Oricymba rhynchocephala Wei Zhang & J. P. Kociolek, 2018

Zhang, Wei, Shang, Guang-Xia, Kociolek, J. Patrick, Wang, Li-Qing & Zhang, Rui-Lei, 2018, Oricymba rhynchocephala sp. nov., a new cymbelloid diatom (Bacillariophyceae) from Xianju National Park in Zhejiang Province, China, Phytotaxa 340 (1), pp. 63-70 : 64-65

Oricymba rhynchocephala Wei Zhang & J. P. Kociolek , sp. nov. ( Figs 1–23 )

LM: valves linear-lanceolate, slightly asymmetrical to the apical axis, with slightly arched valve margins towards rounded and rostrate apices ( Figs 1–14 ). Length 39.0–52.5 μm, width 11.3–13.4 μm, length/width ratio 3.5–4.5, median 4.1 (n= 50). Raphe lateral, external raphe fissures slightly undulate, internal raphe fissures straight. External proximal raphe ends dilated, deflected towards the ventral side. External distal raphe fissures hooked towards dorsal margin. Axial area lanceolate. Central area rhombic-lanceolate, strongly asymmetrical, occupying nearly half the valve width, with 1–2 slightly shortened central dorsal striae, 5–8 shortened central ventral striae. Isolated stigma distinct between the prominent central nodule and the two central striae on the ventral side. Striae moderately radiate, 7–8 in 10 μm in the central part up to 10 in 10 μm in the apices. Areolae visible, 19–23 in 10 μm.

SEM: Valve exterior ( Figs 15–21 ): raphe undulate with proximal raphe ends slightly dilated, weakly bent ventrally ( Figs 15, 16 ), distal fissures hooked, deflected towards the dorsal side ( Figs 15, 19 ). Striae uniseriate, occasionally biseriate in the center on the dorsal side and mantle area ( Figs 16, 18 ). Areolar openings adjacent to the axial area curved or irregular to rounded ( Fig. 16 ); other areolae mostly slit-like, elongate rectangular openings ( Figs 16, 17, 19 ). Small, shallow circular depressions irregular across the axial and central areas ( Fig. 16 ). Longitudinal ridges are very thick along the valve margins except near the valve terminus, and at the apical pore fields, with shallow grooves along both the valve face and mantle edges ( Figs 16, 17, 19 ). The overlapping girdle band is distinct ( Fig. 18 ). The striae of the mantle area are composed of uniseriate or biseriate areolae ( Fig. 18 ). A relative small apical pore field is present at each end on the mantle and clearly separated from the areolae ( Figs 19–21 ).

Valve interior ( Figs 22–26 ): striae formed by slit-like, elongate areolae separated by robust silica ribs ( Figs 23–26 ). The raphe is continuous internally, without separate ends ( Figs 22, 23 ), distal raphe ends offset, bent slightly towards the dorsal margin and terminating in small, knob-like helictoglossae ( Figs 22, 25, 26 ). Two indistinct, narrow, elongate internal stigmal openings on the ventral side occluded by fine ingrowths from the perimeter ( Fig. 23 ).

Type:— CHINA. Zhejiang Provence: Taizhou City, Xianju County, Xianju National Park, Xuedong Stream, 28° 41’ 5” N, 120°28’ 5” E, 299 m a.s.l., June 15, 2016, R. L. Zhang (holotype: SHOU!, slide XJ-XD 36, illustrated in Fig.5 ).

Etymology:—The specific epithet “ rhynchocephala ” refers to the protracted (beak-like) apices that distinguish this species from congeners.

Figures

FIGURES 1–14. Oricymba rhynchocephala, LM, DIC. Valve views, showing variability of the holotype population. Fig. 5 is of the holotype. Scale bar = 10 μm.

FIGURES 15–21. Oricymba rhynchocephala, SEM, external views. 15. Entire valve. Notice the distinct marginal ridge, proximal raphe ends and rounded, single ventrally-placed stigma opening. Striae appear slit-like. Distal raphe ends deflect dorsally. 16. Valve center showing striae, stigma, dilated proximal raphe ends, and shallow circular depressions. 17. High magnification view of the thickened marginal ridge and areolae with small tooth-like projections. 18. View of the valve mantle and overlapping girdle band with a single row of poroids. 19. Rostrate apices with strongly deflected distal raphe end and porellis of the apical pore field positioned entirely on the valve mantle. 20–21. External view of apices showing apical pole fields with porelli that are comprised of small round holes, differentiated morphologically and physically separated from the striae. Scale bars = 10 μm (Fig 15), 5 μm (Fig. 16), 2 μm (Figs 17–19) and 1 μm (Figs 20–21).

FIGURES 22–26. Oricymba rhynchocephala, SEM, internal views. 22. Entire valve with raphe slit evident down the center and a helictoglossa at each apex. 23. Valve centre showing two internal stigma openings each occluded with small, tooth-like projections and small, relatively undifferentiated central nodule without an intermissio. 24. Striae formed by slit-like, elongate areolae separated by robust silica ribs. 25–26. Views of the apices with helictoglossae and apical pore fields evident. Scale bars = 10 μm (Fig. 22) and 2 μm (Figs 23–24) and 5 μm (Figs 25–26).