Hippodonta mudumalaiensis A.Vigneshwaran & B.Karthick, 2022

Vigneshwaran, Anbukkarasu, Wadmare, Neha & Karthick, Balasubramanian, 2022, A new species of Hippodonta Lange-Bertalot, Metzeltin & Witkowski (Bacillariophyceae, Naviculales) from the Western Ghats, India, Phytotaxa 558 (2), pp. 219-228 : 222-223

Hippodonta mudumalaiensis A.Vigneshwaran & B.Karthick sp. nov. ( Figs 2–39 , Fig. 22 represents the holotype)

Description:— LM ( Figs 2–29 ): Cells solitary, valves narrow-lanceolate to rhombic-lanceolate with broadly rounded apices. Valve length 13.0–20.0 μm, width 5.0–6.2 μm (n=67). Axial area narrow-linear, tilted, slightly asymmetric to the apical axis. Central area broadened with short single striae, shorter striae present at any one side; Striae radiate near centre and parallel near apices; no fascia is formed. Raphe linear-filiform, weakly pronounced, small teardrop-shaped and closely spaced central endings. Distal ends of raphe discernible in LM, equally pronounced as central endings, teardrop-shaped. Raphe distal ends positioned before terminal area or weakly advancing into slightly curved towards valve side. Terminal area distinguishable in LM, narrow, lunate and cap-like. Striae coarse, evenly spaced throughout valve, weakly to moderately radiate in the middle, becoming parallel or weakly convergent towards ends, 10–12/10 μm. Lineolae not discernible in LM.

SEM ( Figs 30–39 ): Externally ( Figs 30–34 ), valves with flat face and slightly convex central area ( Figs 30–32 ). Axial area slightly asymmetric ( Fig. 30 ). Proximal raphe endings strongly pronounced, teardrop-shaped and bent towards same side as distal ends ( Figs 31, 32 ). Terminal pores of raphe distinct, advancing towards the terminal area and deflected towards one valve side ( Figs 33, 34 ). Terminal septa clearly developed and bordered by semi circumpolar ( Figs 33, 34 ). Slit-like elongated areolae positioned on apical valve mantle, 40–50 in 10 μm. Striae uniseriate throughout valve, simple apically elongated lineolate, 50–60/10 μm. Rarely near central area transapically elongated lineolate areolae ( Fig. 32 ). Striae in the central area clearly shortened, one side longer than the other side ( Figs 30, 32 ). Prominent hyaline area present throughout the valve mantle ( Fig. 31 ).

Internally ( Figs 35–39 ), striae placed in shallow linear depressions. Areolae covered by hymens. Central raphe endings simple, linear and gradually disappear ( Fig. 38 ). Small wedge-shaped hyaline area present at centre. Distal raphe endings terminate on small defused helictoglossae ( Figs 35, 36, 39 ). Terminal area internally prominent and bordered by hymenated linear depressions ( Fig. 39 ).

Type:— INDIA. Masinagudi, Nilgiris, Tamil Nadu. Stream , 11°33’14.8” N, 76°37’21.6” E, altitude 940 m asl, was collected by Mr. Kannan Govindarajan. (holotype AHMA! Slide #1752 = Fig. 22 ). Type material AHMA #1752 .

Habitat:— Epilithic, submerged stones in the stream. Water chemistry measurements includes pH of 7.35, nitrate (low range, NO 3 –) 0.03 mg ∙L- 1; dissolved oxygen (DO) 6.84 mg ∙L- 1; conductivity: 635 μS∙ cm-1; water temperature: 23.6 °C, total dissolved solids (TDS) 276 mg ∙L- 1.

Etymology:— The specific epithet “ mudumalaiensis ” refers to the name of the location from which this new taxon is identified.

Figures

FIGURES 2–29. Hippodonta mudumalaiensis sp. nov., LM (DIC) from the type material (AHMA #1752). 2–29. Showing the valve variability of the population. Fig. 22 represents the holotype. Scale bar = 10μm.

FIGURES 30–34. Hippodonta mudumalaiensis sp. nov., SEM from the type material (AHMA #1405), external views. 30, 31. Views of the entire valve. 32. Central area. 33, 34. Valve apices. Scale bars = 1 μm (Figs 30–34).

FIGURES 35–39. Hippodonta mudumalaiensis sp. nov., SEM from the type material (AHMA #1405), internal views. 35, 36. Views of the entire valve. 37, 38. Inner central area. 39. view of valve apex end with helictoglossa. Scale bars = 1 μm (Figs 35–39).