Encyonema meghamalaiense V.Vigneshkumar, A.Vigneshwaran, C.Radhakrishnan, B.Karthick & S.Nagaraj, 2025

Encyonema meghamalaiense V.Vigneshkumar, A.Vigneshwaran, C.Radhakrishnan, B.Karthick & S.Nagaraj sp. nov. ( Figs 1–31 View FIGURES 1–20 View FIGURES 21–25 View FIGURES 26–31 ; Fig. 6 View FIGURES 1–20 = holotype)

Description Light microscopy ( Figs 1–20 View FIGURES 1–20 ): Valves lanceolate, asymmetric, slightly dorsiventral in apical axis. Apices protracted, rounded, rostrate to slightly subcapitate ends. Length 16.25–25.6 μm, width 3.78–4.3 μm. Valve Length to breadth ratio 3.78–6.92. Axial area asymmetric, narrow to wide towards central area. Central area, small and shortened striae on either side of the raphe. Raphe lateral to slightly curved. Central raphe ends simple and distal raphe ends curved towards ventral side. Striae radiate, becoming parallel near center area, 14–16 in 10 μm, 15–16 in 10 μm near apices. Areolae irregular, not visible in LM. Stigma absent.

Scanning Electron Microscopy ( Figs 21–31 View FIGURES 21–25 View FIGURES 26–31 ): In external view ( Figs 21–25 View FIGURES 21–25 ), the axial area is narrow to broader towards the central area ( Fig. 22 View FIGURES 21–25 ). Raphe lateral undulates towards the center of the valve ( Figs 21–22 View FIGURES 21–25 ). Central raphe ends simple, slightly curved towards the dorsal side ( Fig. 25 View FIGURES 21–25 ). Distal raphe ends ventrally deflected ( Fig. 23– 24 View FIGURES 21–25 ). Striae irregular, mostly uniseriate but occasionally biseriate ( Figs 21–22 View FIGURES 21–25 ). Transapically, the striae transition to biseriate and sometimes multiseriate arrangements, then return to uniseriate near the raphe ( Figs 23–25 View FIGURES 21–25 ). Near the apices, striae consist of small, lineolate to oval areolae ( Fig. 23 View FIGURES 21–25 ). In internal view ( Figs 26–31 View FIGURES 26–31 ), Striae composed of lineolate to biseriate striae separated by distinct virgae ( Fig. 27 View FIGURES 26–31 ). At each side of the foramen, there are round, small silica depositions present. Central raphe openings not parallel, and one of the central raphe slightly curved towards the dorsal side ( Fig. 26 View FIGURES 26–31 ). Distal raphe ends in helictoglossae. Helictoglossae slightly angled towards the ventral margin ( Figs 29–30 View FIGURES 26–31 ). Girdle bands are highly silicified ( Figs 27–28 View FIGURES 26–31 ).

Type: — INDIA. Meghamalai Lake, Meghamalai, Theni, Tamil Nadu, India ( 9°38ʹ14.7ʺN 77°21ʹ17.4ʺE). Samples were collected by Mr. V. Vigneshkumar and Dr. S. Nagaraj on 25 February 2024. ( Holotype AHMA! Slide #4770 = Fig. 6 View FIGURES 1–20 ). Type material AHMA #4770.

Habitat: —Episammic.

Etymology: —The species epithet meghamalaiense is derived from “Meghamalai,” the mountainous region in Tamil Nadu, India, where this species was discovered. The suffix “-ense” denotes its origin from this specific locality. The name highlights the geographic significance of the Meghamalai Hills as a unique and ecologically important region contributing to diatom diversity.