Geissleria triundulata sp. nov., a new freshwater diatom (Cymbellaceae, Bacillariophyta) from the Mula-Mutha River Basin, India Author Nayak, Pratyasha Biodiversity and Palaeobiology Group, Agharkar Research Institute, Pune, Maharashtra- 411004, India & Affiliated to Department of Botany, Savitribai Phule Pune University, Pune, Maharashtra- 411007, India Author Thacker, Mital Biodiversity and Palaeobiology Group, Agharkar Research Institute, Pune, Maharashtra- 411004, India & Affiliated to Department of Botany, Savitribai Phule Pune University, Pune, Maharashtra- 411007, India Author Hamilton, Paul B. 0000-0001-6938-6341 Research and Collection, Canadian Museum of Nature, Ottawa, ON K 1 P 6 P 4, Canada PHAMILTON@nature.ca Author Karthick, Balasubramanian 0000-0003-4066-2458 Biodiversity and Palaeobiology Group, Agharkar Research Institute, Pune, Maharashtra- 411004, India & Affiliated to Department of Botany, Savitribai Phule Pune University, Pune, Maharashtra- 411007, India karthickbala@aripune.org text Phytotaxa 2024 2024-07-25 661 1 109 119 http://dx.doi.org/10.11646/phytotaxa.661.1.9 journal article 300742 10.11646/phytotaxa.661.1.9 5fd60f0d-7104-4ee1-97a7-81f7ccdd2d78 1179-3163 13218342 Geissleria triundulata P.Nayak, M.Thacker & B.Karthick sp. nov. ( Figs 1–40 , Fig. 3 represents the holotype ) Description:—LM ( Figs 3–26 ): Valves linear-lanceolate, with slightly triundulate margins and weakly protracted, broadly rounded apices. Length 16.0–23.5 µm, width 5.5–6.5 µm (n=60). Raphe filiform, straight. Axial area narrow and linear, slightly widening towards centre of valve. Central area rectangular, formed by one shortened stria on each valve side. Middle striae located at considerable distance from neighbouring two. An isolated stigma present near central nodule. Proximal raphe ends straight and slightly enlarged. Distal raphe endings not discernible in LM. Striae slightly radiate to subparallel throughout, alternatively longer and shorter around central nodule, 22–24 in 10 µm. Areolae not discernible in LM. Annulus barely discernible in LM. SEM ( Figs 27–40 ): Externally raphe branches straight and filiform ( Fig. 27 ). Proximal raphe endings slightly, roundly enlarged ( Figs 27, 32–33 ). Distal raphe ends hooked and curved in same direction at apices and continue on valve mantle ( Figs 27–29 ). Axial area narrow, linear, and widened towards rectangular central area, defined by one shortened stria on each side of valve. A single isolated slit-like stigma present close to central nodule. Central area hyaline and slightly elevated ( Figs 32–33 ). Striae uniseriate composed of transapically elongated lineolate areolae, around 90 in 10 μm. A pair of sub-polar areolae present at both sides of the raphe at valve ends ( Figs 28–29 ). Presence of slit-like transapically elongated structure at apices ( Figs 30–31 , arrowheads). Internally, entire valve showing organisation of striae, location of stigma and remnants of copulae ( Fig 34 ). Proximal raphe endings slightly hooked and deflecting on same side, terminating onto central nodule of protruding sternum ( Figs 37–38 ). Distal raphe endings terminate in small helictoglossae ( Figs 35–36 ). Virgae raised between slightly sunken striae ( Figs 37–38 ). Warty outgrowths along the long sides of the sub-polar areolae present ( Figs 39–40 , arrowheads). Type :— INDIA . Maharashtra : Pune, Mutha River, near Jambhali, 18.388833°N , 73.650861°E , 580 m . a.s.l, 25 May 2022 . ( Holotype AHMA ! 3776 = Fig. 3 ). FIGURES 3–26. Geissleria triundulata sp.nov . , light microscope images showing size diminution series: (3) holotype specimen. Scale bar = 10 μm. 3776/ 51. FIGURES 27–33 . Geissleria triundulata sp.nov. , External valve views: (Fig. 27) External view of an entire valve with straight and filiform proximal raphe endings; (Figs 28–29) Details of apices in external view presenting elongated subpolar areolae with distal raphe ends hooked in the same direction; (Figs 30–31) 1) Details showing the organisation of striae between the annuli and axial area, 2) Presence of slit-like transapically elongated structure at both sides of each apex (arrowheads); (Figs 32–33) Details of the central area showing the enlarged proximal raphe endings and presence of an isolated stigma. (Fig. 33) Central area is hyaline and slightly elevated. Scale bars = 1μm. 3776/ 51. FIGURES 34–40 . Geissleria triundulata sp.nov. , Internal valve views: (Fig. 34) Internal view of an entire valve showing the organisation of striae, location of stigma and remnants of the copulae; (Figs 35–36) Distal raphe ends terminating into small helictoglossae; (Figs 37–38) Proximal raphe endings are slightly hooked and deflecting on the same side, and showing somewhat sunken striae; (Figs 39–40) Presence of warty outgrowths along the long sides of the subpolar areolae at the apices. Scale bars = 1μm. 3776/ 51. Habitat :—Epilithic sample collected from the river bank. Etymology :—The specific epithet “ triundulata ” refers to the valve outline of the species. Ecology and distribution :— G . triundulata sp. nov. was found in low electrical conductivity (59.2 µs/cm) and slightly alkaline pH (7.95) waters. The dominant genera in the sample are Pantocsekiella K.T.Kiss & Ács (2016: 62) , Fragilaria Lyngbye (1819:185) , Sellaphora (Mereschkovsky 1902: 187) , and Navicula . As of now, this taxon is known only from the type locality.