Lacustriella acutocuneata Metzeltin, Lange-Bertalot & Kulikovskiy 2012

Rodionova, Yelena V., Pomazkina, Galina V. & Sherbakova, Tatyana A., 2024, Two new species of the genus Lacustriella (Bacillariophyta) from Lake Baikal, Phytotaxa 652 (4), pp. 261-272 : 264

Lacustriella acutocuneata Metzeltin, Lange-Bertalot & Kulikovskiy 2012

Light microscopy (LM): ( Figs 47–56 ). Valves linear-elliptic-lanceolate with slightly concave margins and rostrate apices. Valve length 48.5–67.0 μm, width 18–19 μm. External axial area narrow at apices, gradually expanding into the weakly defined central area. Raphe filiform, central endings straight, terminal ends bent to opposite sides. Striae uniseriate, slightly radial proximally, become radial towards apices, 11–12 in 10 μm. One longitudinal canal along each margin.

Scanning electron microscopy (SEM): ( Figs 57–64 ). Externally, areolae in striae small, round, open, in depressions, 12–15 in 10 μm, slightly irregular in the central part of the valve. Proximal areolae near axial and central areas enlarged, rounded ( Fig. 58 ). Distal areolae along the longitudinal canals appear binary due to narrowed vimines ( Figs 58, 59 ), with the outer ones somewhat larger and elongate. The surface of longitudinal canals is smooth, unornamented ( Fig. 58 ). Proximal raphe endings lay in slightly elongated drop-shaped depressions ( Fig. 59 ). Distal endings smoothly curved to opposite sides and onto the mantle ( Figs 61, 62 ). Internally, areolae in striae covered with hymenes. Raphe endings terminate on helictoglossae, central helictoglossae merged ( Figs 63, 64 ).

The species was commonly observed in many sites of all three basins of Lake Baikal, including Anga Bay, the vicinity of Cape Khoboi on Olkhon island, near Сape Tonkiy and the area of Cape Kabaniy.

Figures

FIGURES 47–56. Lacustriella acutocuneata. LM. Figs 47−56. Valve views.

FIGURES 57−64. Lacustriella acutocuneata. SEM external (Figs 57–59, 61–62) and internal views (Figs 60, 63–64). Fig. 57. Valve view. Fig. 58. Smooth surface of the longitudinal canal, morphology of areolae bordering the canal. Fig. 59. Central area with proximal raphe endings; areolae in striae; a row of enlarged areolae along the axial area. Figs 61–62. Distal raphe endings. Fig. 60. Valve view. Fig. 63. Central nodule, proximal raphe endings terminating in merged helictoglossae. Fig. 64. Distal raphe end with a helictoglossa. Scale bars = 10 μm (Figs 57, 60); 5 μm (Figs 59, 61−64); 2 μm (Fig. 58).