Oricymba tianmuensis W. Zhang

Zhang, Wei, Li, Yan-Ling, Kociolek, J. Patrick, Zhang, Rui-Lei & Wang, Li-Qing, 2015, Oricymba tianmuensis sp. nov., a new cymbelloid species (Bacillariophyceae) from Tianmu Mountain in Zhejiang Province, China, Phytotaxa 236 (3), pp. 257-265 : 258-261

Oricymba tianmuensis W. Zhang & Y.-L. Li, sp. nov. ( Figs 1–25 )

LM: valves linear-lanceolate, symmetrical or slightly dorsiventral, with an inflated, gibbous central portion gradually tapering or nearly parallel to bluntly-cuneate poles ( Figs 1–9 ). Length 28–74 μm, width 11–15 μm, length/width ratio 3.0–4.8, median 3.6 (n=35). Raphe slightly lateral, external raphe fissures slightly undulate, internal raphe fissures straight. Proximal endings of raphe widened, deflected towards the ventral side. External distal raphe fissures hooked towards dorsal margin. Axial area lanceolate. Central area rhombic-lanceolate, strongly asymmetrical, near to half the valve width, with 1–2 slightly shortened central dorsal striae, 4–8 shortened central ventral striae. Isolated stigma distinct between the central nodule and the two central striae on the ventral side. Striae slightly radiate becoming moderately radiate near the poles, 7–9 in 10 μm. Areolae visible, 20–25 in 10 μm, median 22 in 10 μm (n=45).

SEM: valve exterior ( Figs 11–18 ): raphe undulate with proximal raphe fissures slightly dilated, weakly bent ventrally ( Figs 11, 15 ), distal fissures hooked, deflected towards the dorsal side ( Figs 11, 13, 14 ). Striae uniseriate, occasionally biseriate, extending onto the mantle ( Figs 11–18 ). Areolar openings adjacent to the axial area curved, triangular or elongate; other areolae variable in shape, most slit-like, elongate rectangular openings ( Figs 11–18 ). Small, shallow circular or slightly atypically circular depressions irregular across the axial and central areas ( Fig. 15 ). 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 13–17 ). A relative small apical pore field is present and clearly separated from the areolae ( Figs 13–14 ). The epicingulum is distinct in the girdle ( Figs 12, 17 ). The striae of the mantle area are composed of five rows of areolae, both uniseriate or biseriate ( Fig. 18 ). Valve interior ( Figs 21–25 ): striae formed by slit-like, elongate areolae separated by robust silica ribs ( Figs 21–25 ). Internal proximal raphe endings hidden by an overgrowth of silica, distal raphe ends offset, bent slightly towards the dorsal margin and terminating in small, knob-like helitcoglossae ( Figs 21–25 ). Two indistinct, narrow, elongate internal stigmal openings on the ventral side occluded by fine ingrowths from the perimeter ( Fig. 24 ).

Type:— CHINA. Zhejiang Provence: Tianmu Mountains, Tianmu Canyon, 30° 21’ 56” N, 119° 28’ 35” E, 655 m a s.l., W. Zhang, s.n. (holotype: SHOU!, slide ZW-ZheJ 0023, illustrated in Fig. 3 ).

Etymology:— Oricymba tianmuensis is named after the type locality.

Observations:— A very different individual with odd striae was observed in our study ( Figs 19–21 ). The outline of valve, raphe course, and number of striae in 10 μm all conform to conditions of “normal” individuals. It is interesting that the striae show a strong tendency to become biseriate, with circular, lateral elongate or irregularly triangular areolae ( Figs 20, 21 ).

Figures

FIGURES 1–10. Oricymba tianmuensis, LM, DIC. 1–9. Valve views, showing the valve variability of the holotype population. 10. Girdle view. Scale bar = 10 μm.

FIGURES 11–18. Oricymba tianmuensis, SEM. 11. External view of a whole valve. 12. Girdle view. 13–14. External view of pole with apical pole field. 15. External view of valve center showing striae, stigma and shallow circular impressions. 16. Details of a fractured ridge. 17. Girdle view of pole showing ridge and groove. 18. Details of striae and external areola openings in the girdle. Scale bars = 20 μm (Figs11–12), 2 μm (Fig. 13), 3 μm (Fig. 14), 5 μm (Figs 15–17) and 1 μm (Fig. 18).

FIGURES 19–21. Oricymba tianmuensis (teratological form), SEM. Fig. 19. External view of a whole valve. 20. External view of valve center showing uniseriate-biseriate striae and stigma. 21. External view of pole with raphe endings. Scale bars = 20 μm (Fig. 19), 5 μm (Fig. 20) and 10 μm (Fig. 21).

FIGURES 22–25. Oricymba tianmuensis, SEM. Internal view of a whole valve. 24. Internal view of valve centre showing internal stigma openings. 25. Internal view of the pole with helictoglossae and apical pore field. Scale bars = 20 μm (Figs 22, 23) and 5 μm (Figs 24, 25).