Diploneis mawsmaii, Bhatt & Karthick, 2020

Bhatt, Chintan & Karthick, Balasubramanian, 2020, A new aerophilic species of the genus Diploneis (Bacillariophyta) from the Mawsmai cave of Meghalaya, Northeast India, Phytotaxa 443 (1), pp. 67-78 : 70-72

Diploneis mawsmaii sp. nov. (Figs 2–29)

Description

LM (Fig 2–17): Valves lanceolate-elliptical to linear-elliptical with broadly rounded apices. Valve length 12.5–27.5 μm and width 6.5–8.5 μm. Axial area lanceolate and narrow. Longitudinal canals linear-lanceolate, narrow, narrowing towards the valve poles and slightly expanding at the central area. Central area widely expanded, approximately circular to oval 1.8–2.7 μm wide. Raphe linear, obscurely or faintly resolvable in LM, distal ends deflected in the same direction especially seen in larger valves (Figs 2, 3). Transapical striae radiate, becoming parallel at central area. Striae density 23–26 in 10 µm. Areolae not discernible in LM.

FIGURES (2–17). LM valve views of Diploneis mawsmaii , representing the size diminution series. All individuals are from the type location. (Scale bar represents 10 μm).

SEM, external (Figs 18–23): Valve face flat with superficial transapical undulations and depressions formed by alveoli (Figs 18, 19). Externally, raphe straight and linear with proximal ends shortly bent unilaterally in same direction (Fig. 19). Distal ends deflected towards the mantle in same direction as proximal ends (Figs 20, 21). Striae biseriate becoming multiseriate near valve margin. Alveolus opens externally through 3–4 rows of small, round, pin-point areolae, often decreasing in number near longitudinal canals (Fig. 22, white arrow). 5 to 8 shorter striae at central area showing the discontinuation of areolae at midway towards longitudinal canals (Fig. 22, indicated by “S”). Longitudinal canals with single row of simple, small, irregularly placed round areolae not like striae areolae (Fig 22, black arrow). The central area largely expanded bearing a prominent circular to oval, central nodule which separates the proximal raphe ends (Fig. 19). Cingulum composed of two bands: the valvocopula and a pleura (Fig. 23).

SEM, Internal (Fig 23–30): Internally, longitudinal canals narrow throughout the valve (“a” on Fig. 24), except slightly extended transapically at central area (“b” on Fig. 24). The raphe fissures straight, narrow and linear with simple termination at proximal and the distal ends (Figs 25, 26, 27) Alveoli shorter at central area becoming acute or tapering at ends towards the longitudinal canals forming a wedge-shaped outline (Fig 28). Alveoli occluded by thin obscure silicate layer (Fig 29 ‘c’). Broken alveolus feebly shows transapical costae interconnection (Fig. 29 ‘d’). Valvocopula band with a serrated advalvar edge (Fig. 30).

FIGURES (18–23). SEM external valve views: Fig. 18. View of the whole valve, Fig. 19. Valve surface showing transapical undulations and depressions (marked with an arrow) and proximal raphe ends slightly bent in one direction, Fig 20 & 21. Distal raphe ends turned longer in the same direction, Fig. 22. Short striation in the central area with simple rounded areolae, marked as ‘S’, white arrow shows areolae of longitudinal canal and black arrow shows areolae of striae, Fig 23. Valve apices showing the valvocopula and the pleura, Scale bars = 2 μm (Fig. 18); 1 μm (Figs 19, 20, 21, 22, 23)

FIGURES (24–30). SEM internal valve views: Fig. 24. View of the whole valve showing the longitudinal canals located on either side of the raphe; the narrow part of the canal is marked with an arrow ‘a’ and the flattening of the canal at the central area is marked with an arrow ‘b’, Fig. 25. Proximal raphe ends with a simple termination, Fig. 26 & 27. Distal raphe with a simple termination, Fig. 28. The short alveoli at the central area showing acute or tapering ends Fig. 29. Alveoli with thin obscure occlusions and a broken alveolus in which the transapical costae connection are visible (marked with an arrow head c & d, respectively), Fig. 30. View of a whole valve, showing the broken serrated band of the valvocopula. Scale bars = 2 μm (Fig 24); 1μm (Figs 25, 26, 27, 28, 29, 30)

Type (designated here): — INDIA. Mawsmai cave, Cherrapunji, Meghalaya, India 25.24457 °N 91.72405°E ;. Epibryophytic sample collected on 05 August 2018 near the exit of the cave by Mr. Radhakrishnan Cheran (Holotype: AHMA! Individual in Slide No 2027 – 01 from material #2027, here represented as Fig. 2; Isotype: CAL /ALG. 58, Central National Herbarium Botanical Survey of India, Kolkata , India.

Type habitat: Mosses growing on moist rocky walls of cave.

Etymology: —The specific epithet refers to the type locality, Mawsmai cave.