Cymbella liyangensis Zhang, Jüttner & E.J. Cox, 2018

Zhang, Wei, Jüttner, Ingrid, Cox, Eileen J., Chen, Qiao & Tan, Hongxin, 2018, Cymbella liyangensis sp. nov., a new cymbelloid species (Bacillariophyceae) from streams in North Tianmu Mountain, Jiangsu province, China, Phytotaxa 348 (1), pp. 14-22 : 16

Cymbella liyangensis Zhang, Jüttner & E.J. Cox sp. nov. ( Figs 2–16 )

LM: Valves semi-lanceolate, moderately dorsiventral, dorsal margin moderately arched, ventral margin slightly convex, larger specimens slightly tumid in central section of ventral margin. Ends not protracted or only very slightly, broadly to obtusely rounded ( Figs 2–6 ). Length 44.5–66.5 μm, width 11.0–14.5 μm, length/width ratio 3.6–4.5 (n=26). Axial area narrow, nearly linear, slightly widening towards valve centre in larger specimens. Central area indistinct or very small, bordered on dorsal side by 1–2 shorter central striae. Raphe not, or only slightly ventrally displaced, distinctly lateral, filiform near distal ends and strongly reverse-lateral near proximal ends. Striae very slightly radiate, more radiate near valve ends. Stria density 7–8 in 10 μm (mostly 7 in 10 μm dorsally and 8 in 10 μm ventrally), slightly denser towards valve ends (9–11 in 10 μm, mostly 10 in 10 μm); striae areolate, 19–22 areolae in 10 μm. 3–4 stigmata close to central striae on ventral side. Size of stigmata varies, sometimes not very distinct from stria areolae ( Figs 2–4 ).

SEM: Valve face flat, separated from mantle by a small marginal ridge. Ridge protrudes over mantle with no grooves ( Figs 10–12 ). Externally raphe displaced dorsally, curving ventrally near valve centre and terminating in drop-shaped proximal ends, not, or only weakly, deflected ( Figs 8–10 ). Close to valve apices raphe curves slightly ventrally, but terminal fissures deflected to dorsal side of valve at an angle of almost 90° ( Figs 8, 11, 12 ). Usually four (sometimes three) stigmata adjacent to ventral striae, with round external openings and short transapically elongate internal openings, marked by small marginal nodules ( Figs 9, 10 , 14 ). Transapical striae composed of apically orientated slit-like areolae, often round areolae adjacent to the axial and central area ( Figs 8–10 ). Striae can be partially biseriate and up to 10 fully biseriate, rarely multiseriate, towards valve apices, with round areola openings ( Figs 11, 12 ). No pore occlusions were seen. Virgae thickened internally and wider towards valve centre. Apical pore fields composed of vertically aligned porelli at both apices ( Figs 11, 12 ). Internally proximal raphe endings hidden by an overgrowth of silica, distal raphe ends offset, bent slightly towards dorsal margin, terminating in small helictoglossae ( Figs 13–16 ).

Type: — CHINA. Jiangsu Province: Liyang City, North Tianmu Mountain, Pingqiao stream, 31° 12′ 34′′ N, 119° 26′ 52′′ E, elevation 87 m a.s.l., samples collected by Q. Chen (holotype: slide THCZ- Pingqiao, holotype specimen illustrated in Fig. 3 ).

Etymology: —The specific epithet “ liyangensis ” refers to Liyang City which is close to the site where the new species was collected.

Figures

FIGURES 2–7. Cymbella liyangensis, LM (DIC). Figs 2–6. Valve views, showing the valve variability of the holotype population. Fig 7. Light micrographs showing the biseriate areolae at the apices. Scale bar = 10 μm (Figs 2–6), Scale bar = 2 μm (Fig. 7).

FIGURES 8–12. Cymbella liyangensis, SEM, external views. Fig. 8. External view of a whole valve with a ridge-like structure at the junction of valve face and mantle. Figs 9–10. External view of valve center showing striae composed of slit-like areolae, becoming round and biseriate close to axial area, varied shapes of stigmata and the proximal raphe endings. Figs 11–12. Showing the biseriate striae at the apices, ridge-like structure and pore field. Scale bars = 10 μm (Fig 8), 5 μm (Figs 9–12).

FIGURES 13–16. Cymbella liyangensis, SEM, internal valve views. Fig. 13. Internal view of a whole valve. Fig. 14. Internal view of valve centre showing internal stigma openings. Figs 15, 16. Internal view of valve ends with dorsally curved, knob-like helictoglossae and the biseriate to multiseriate striae. Scale bars = 10 μm (Fig 13), 5 μm (Fig 14), 2 μm (Figs 15, 16).