Epithemia agharkarii A. Vigneshwaran, J.P. Kociolek & B. Karthick, 2021

Vigneshwaran, Anbukkarasu, Liu, Yan, Kociolek, John Patrick & Karthick, Balasubramanian, 2021, A new species of Epithemia Kützing (Bacillariophyceae, Rhopalodiales) from the Mula river, Western Ghats, India, with comments on the phylogenetic position of Rhopalodia and Epithemia, Phytotaxa 489 (2), pp. 171-181 : 172-174

Epithemia agharkarii A. Vigneshwaran, J.P. Kociolek & B. Karthick sp. nov. ( Figs 1–40 , Fig. 20 represents the holotype)

Description:—LM ( Figs 1–28 ): Valves dorsiventral, asymmetrical to the apical and transapical axis. Convex dorsal margin and almost straight ventral margin. Frustules asymmetrical ( Figs 22, 23 ) lanceolate to slightly elliptic in girdle view. Apices slightly rounded, somewhat bent ventrally. Valve length 16–38 µm, valve breadth 4.5–6.3 and frustule breadth 12.5–17.5 µm (n=84). Valve Length to breadth ratio 3.5–6. Primary fibular costae distinct and weakly radiate, 2–4 in 10 μm. Striae densities 14–15 in 10 μm, parallel in middle and radiate towards the ends. Areolae visible in LM, 12–16 in 10 μm. Terminal thickenings of the transapical costae evident in girdle view ( Fig. 24 ). Raphe difficult to observe, extending from near the ventral margin at the apices to nearly the dorsal margin in the center ( Figs 3, 20 and 28 , arrows).

SEM ( Figs 29–40 ): External views (29–36) show valves in girdle view being asymmetrical to the apical axis ( Fig. 29 ). Raphe visible ( Fig. 29 , arrows), extending from the ventral margin of the valve face to the dorsal margin in the center of the valve ( Figs 29, 30 , arrows), with straight proximal raphe ends ( Fig. 30 , arrows), distal raphe ends dorsally deflected and ended in a distinct poroid. ( Fig. 31 , arrow; Fig. 32 ). Keel absent, raphe with thin border ( Figs 30–31 , arrowheads). Striae radiate, biseriate, composed of C-shaped openings arranged in groups of 4 (more or less) and every pair of areolae opposite to each other ( Fig. 33 ; Fig. 34 , arrows). On the valvocopula a single row of poroids is present ( Fig. 32 , arrows). Cingulum elements 4–6 ( Fig. 35 , asterisks). Internally ( Figs 37–40 ), valves show robust primary ( Fig. 37 , arrows) and thinner secondary fibular costae ( Fig. 37 , arrowheads). Internally, rib-like siliceous extensions present transapically ( Fig. 38 , asterisks). From the middle, costa size becomes smaller towards apices. Primary and secondary fibular costae are continuous from dorsal to ventral valve margin ( Figs 37, 38 ) across the raphe canal ( Fig. 40 , arrows). In each secondary fibular costa alveolus, a single row of areolae is present. Each alveolus includes 4 (more or less) C-shaped areola foramina ( Fig. 39 , arrows) with virgae, vimines and alveolus ( Fig. 39 , asterisks). The C-shaped foramina make a depression in the areolae. The canal raphe ( Fig. 39 , arrowheads) extends from the ventral to the dorsal side across the valve face ( Fig. 37 arrowheads, Fig. 40 arrows and arrowheads). Proximal and distal raphe endings straight ( Fig. 39 , arrowheads).This raphe canal divides the areolae rows into two sections. On the raphe canal, portulae are irregularly-shaped ( Fig. 40 , arrowheads).

Type:— INDIA. Mulshi, Pune, Maharashtra. Mula River , 18°31’53.1” N, 73°30’57.7” E. 574 m asl, Mr. Samadhan Pardhi on 6th January 2017 (holotype AHMA! Slide #1405 = Fig. 20 ). Type material AHMA #1405 .

Habitat:—Epilithic, submerged stones in Mula river. Environmental measurements include a pH of 7.02, total phosphorus (TP) of 0.21 mg ∙L- 1, total nitrogen (TN) 0.1 mg ∙L- 1; dissolved oxygen: 6.55 mg ∙L- 1; conductivity: 78.4 μS∙ cm-1; water temperature: 34.3 °C, total dissolved solids (TDS) 46 mg ∙L- 1.

Etymology:—This species epithet is dedicated to the late Professor S.P. Agharkar, founding Director of the Agharkar Research Institute in Pune and a remarkable botanist, for his contribution to the field of Phytogeography.

Figures

FIGURES 1–28. Epithemia agharkarii sp. nov., LM (DIC) from the type material (AHMA #1405). 1–28. Valves, focused on the ventral part of the valve face, showing the valve variability of the population. 4–5. Same valve showing fibular costae. 21–26. Frustule focused on the ventral girdle view of the frustule variability of the holotype population. Fig. 20 represents the holotype. Figs 3, 20, and 28. In LM view, arrows showing the raphe, extending from near the ventral margin at the apices to nearly the dorsal margin in the center. 24. In LM view, arrows indicating the terminal thickenings of the transapical costae. Scale bar = 10 μm, Figs 1–20 (Fig. 8) & 21–28 (Fig. 21).

FIGURES 29–34. Epithemia agharkarii sp. nov., SEM from the type material (AHMA #1405), external views. 29. External view of the ventral frustule, raphe (arrows) and the girdle bands. 30. Valves are showing the proximal end of the raphe with a small circular opening (arrows) and arrowheads showing the absence of keel. 31. The distal raphe end deflected dorsally (arrow) and arrowheads showing the absence of keel. 32. A broken frustule is showing the striation of the external valve, and a single row of poroids (arrows) on the valvocopula. 33, 34. Valves are showing the C-type areolae foramina (arrows). Scale bar = 2 μm (Figs 29, 32), 1 μm (Figs 30–31, 33), 0.5 μm (Fig. 34).

FIGURES 35–40. Epithemia agharkarii sp. nov., SEM from the type material (AHMA #1405), external and internal views. 35, 36. Dorsal frustule showing a regularly sculptured outer surface (Fig. 35, arrows) of the valve with C-type foramina, single row of poroids on the valvocopula and cingulum elements (Fig. 35, asterisks). 37. Ventral view of valve internal with primary (arrows) and secondary fibular costae (arrows), alveolus. 38. Internal view showing the siliceous extensions of the ribs indicated by asterisks. 39. Magnified view of primary fibular costae inside with secondary fibular costae, alveolus (asterisks), C-shaped foramina (arrows), silica processes, and irregularly shaped portula with internal raphe (arrowheads) inside the canal. 40. Broken valve showing the raphe canal (arrows), portula (arrowheads) and stright distal raphe ending. Scale bar = 10 μm (Fig. 35), 2 μm (Fig. 36), 4 μm (Figs 37, 38, 40), 1 μm (Fig. 39).