Cymbella distalebiseriata Bing Liu et D.M. Williams, 2018

Liu, Bing, Williams, David M. & Liu, Qingyu, 2018, A new species of Cymbella (Cymbellaceae, Bacillariophyceae) from China, possessing valves with both uniseriate and biseriate striae, Phytotaxa 344 (1), pp. 39-46 : 41-44

Cymbella distalebiseriata Bing Liu et D.M. Williams , sp. nov. ( Figs 1–40 )

LM:

Valves asymetrically lanceolate, strongly dorsiventral; dorsal side strongly convex, ventral side straight or slightly convex ( Figs 1–14 ); larger specimens slightly tumid at centre ( Figs 1–2 ). Apices not protracted, cuneate to bluntly rounded, subrostrate on some specimens; valve length 38–62 μm, breadth 8–12 μm, maximal length/breadth ratio 5.6 (n = 29). Axial area narrow, linear, central area absent. Raphe located near valve centre, becoming filiform at terminal ends, reverse-lateral when approaching central ends ( Figs 1–3 ). Striae slightly radiate at centre of valve, becoming more radiate towards apices. Stigmata 2–3, striae 7–9 in 10 μm on dorsal central side (often 8 in 10 μm), 8–10 in 10 μm on ventral central side (often 9 in 10 μm), 9–11 near apices. Puncta not resolved in LM.

SEM:

Frustule and girdle view: Frustule rectangular in ventral view girdle; frustule composed of epivalve, hypovalve and four girdle bands ( Figs 15, 17, 18 ). Striae extending onto deep mantle with interruptions along valvar margin, terminating halfway ( Figs 15–18 ). Some biseriate striae emerging from uninseriate striae on mantle, complete biseriate striae near apices, with corresponding biseriate striae on mantle ( Figs 17–18 , 24, 28, 31 ). Four open girdle bands present ( Figs 15, 17, 18 ), composed of valvocopula and three smaller copulae.

External view: Central pores present, elongate, bent slightly towards ventral side, terminal raphe fissures deflexed dorsally almost 90 ° to apical axis, not bisecting apical pore fields ( Figs 19–22 ). Stigmata 2–3 at ends of ventral central striae, ca. 3 to 11 ( Figs 23–31 ) biseriate striae distributed near apices ( Figs 19–22 , arrows). Puncta lineolate in uniseriate striae, rounded in biseriate striae, with lineolate puncta 25–30 in 10 μm—some mixed, composed of both double and single rows of puncta, in places grading between uniseriate and biseriate (e.g. Figs 24, 26, 28–31 ). Externally, structure and shape of areolae in biseriate striae similar to that found in apical pore fields ( Fig. 22 ). Apical pore field composed of ca. 7–9 rows and 15–17 pervalvar axis columns, not bifurcated by terminal raphe fissure (e.g. Figs 17 , 26, 31 ).

Internal view: Raphe almost located at valve centre, terminal raphe end terminated in helictoglossa, proximal raphe ends invisible, obscured by hooded siliceous structure ( Fig. 32–36 ). Striae alveolate, in part, 2–3 stigmata obscured with internal occlusions ( Fig. 33–36 ). Biseriate striae between 3 and 11 ( Figs 37–40 ), some mixed as above (e.g. Figs 37–40 ).

Type: — CHINA. Hunan: Yuan Ling County, Shenxi River, sampling point, 28°44’48” N, 110°25’27” E, 200 m a.s.l., Bing Liu , 17 th March 2017 (holotype BM! 101409 = Fig. 3 ; isotype JIU! G201701 = Fig. 5 ) .

Etymology: —The epithet ‘ distalebiseriata ’ is a composite of ‘distal’ and ‘biseriate’, referring to the biseriate striae that occur near both poles.

Ecology: —The following environmental parameters were measured in the field: Conductivity 215.7 ± 2.6 μS/cm, pH was 8.3 ± 0.1, water temperature 12.2 ± 0.1 °C.

Figures

FIGURES 1–14. Cymbella distalebiseriata sp. nov., LM. 1–14. Fourteen valves showing size diminution series. 3. Micrograph of holotype specimen. 5. Micrograph of isotype specimen. Scale bar =10 μm (in Fig. 1) for all figures.

FIGURES 15–18. Cymbella distalebiseriata sp. nov., frustule and girdle view, SEM. 15. Frustule in ventral girdle view. 16. Frustule in side view, note deep mantle on dorsal side. 17–18. Details of Fig. 15, showing apical pore fields, girdle bands and some biseriate striae with their corresponding uniseriate striae on mantle (arrows). Scale bars =10 μm (Figs 15–16), 5 μm (Figs 17–18).

FIGURES 19–22. Cymbella distalebiseriata sp. nov., external view, SEM. 19–22. Four valves showing valve outline, raphe shape and some biseriate striae distributed near both apices (arrows). Scale bars =10 μm.

FIGURES 23–31. Cymbella distalebiseriata sp. nov., external view, SEM. 23–31. Nine apices showing details of biseriate striae. Scale bars = 5 μm.

FIGURES 32–36. Cymbella distalebiseriata sp. nov., internal view, SEM. 32. A whole valve. 33–36. Four central parts of the valves, showing two to three stigmata (curved arrows) and obscured intermission (arrows). Scale bars =10 μm (32), 5 μm (33–36).

FIGURES 37–40. Cymbella distalebiseriata sp. nov., internal view, SEM. 37–40. Four apices showing biseriate striae. Scale bars = 5 μm.