Cosmarium hiranoi Anissimova & Kutuzova, 2025

Anissimova, Olga V. & Kutuzova, Irina A., 2025, Cosmarium hiranoi sp. nov (Zygnematophyceae, Desmidiaceae): a new desmid species from a lake in Oasis Larsemann Hills (East Antarctica), Phytotaxa 712 (1), pp. 81-86 : 83-85

Cosmarium hiranoi Anissimova & Kutuzova , sp. nov. ( Figs. 2A , 3A ).

Synonyms: — Cosmarium clepsydra var. depressum Hirano Memoirs of the National Institute of Polar Research, Special Issue 11: 23, pl. 3: figs 18, 19, 1979; C. clepsydra var. granulatum Hirano Memoirs of the National Institute of Polar Research, Special Issue 11: 22, pl. 3: fig. 17; C. clepsydra var. undulatum Hirano Memoirs of the National Institute of Polar Research, Special Issue 11: 22, pl. 3: figs 14, 15.

Diagnosis: —Cells in frontal view longer than broad, with a deep linear sinus, closed for the greater part. The semicells in outline have a broad trapeziform shape, with convex, sometimes slightly undulate sides, widely rounded angles and a slightly elongated, notched apex. Semicells in apical view ellipsoid with a tubercular median inflation and widely rounded sides. Cell wall is wrinkled. Cell wall pores are evenly spaced at a distance of about 2-3 µm from each other. Zygospores are not known. Cell dimensions: length 20‑31 μm, breadth 18‑26 μm, isthmus 3.9‑4.4 μm (n=20).

Type:— EAST ANTARCTICA, Oasis Larsemann Hills: Stepped lake, 69°22’34.83”S, 76°22’59.30”E, algae-bacterial mats, I. Kutuzova, 16 January 2023, (holotype: MW!, preserved as a fixed natural sample “vod160”, in Algae collection ( MW) of the Department of Mycology and Algology of Moscow State University, Russian Federation). Morphology of vegetative cell of the holotype sample is illustrated in Figs. 2A, B, C .

Type locality:—Freshwater Stepped lake, algae-bacterial mats, Oasis Larsemann Hills, East Antarctica (69°22’34.83”S, 76°22’59.30”E).

Registration:—http://phycobank.org/105749

Etymology:—The species name is dedicated to the Japanese phycologist and desmidiologist Minoru Hirano (1910−1994), who first discovered the cells of this species of algae.

Distribution and ecology:—The taxon is known from Stepped lake in the area of Progress Station (East Antarctica, Oasis Larsemann Hills, Broknes Peninsula). It was found in samples of periphyton, in 2023. The water in the lake had the following characteristics: pH 6.0 –7.0, total dissolved solids levels of 372–442 mg /l, conductivity of 702–820 µS/cm and temperature 1,7–9°С. According to literature data, this species was found (as Cosmarium clepsydra ) in the lakes Yukidori Zawa and O-ike of eastern part of the island West Ongul in the Lützow-Holm Bay ( Hirano 1979; Oguni & Takahashi 1989) and in four lakes of Progress Station of the Broknes Peninsula ( Luknitskaya 2020).

Differential diagnosis:—In general outline, in the frontal view, the cells of C. hiranoi are similar to Cosmarium fontigenum Nordstedt in Wittrock & Nordstedt (1878: 71), from which it differs in its wrinkled membrane and the presence of a wart in the center of each semicell. In the apical view, C. hiranoi is similar to C. phaseolus var. elevatum Nordstedt (1873: 17) , but the latter in frontal view does not have and a slightly elongated, notched apex at the semicells.

Figures

FIGURE 2. Light microscope images of cells of Cosmarium hiranoi sp. nov. (A-C) from the Oasis Larsemann Hills (Antarctica) and C. clepsydra (D-F) (from Murmansk region). A, D) Vegetative cells frontal view, B, E) Vegetative cells lateral view. C, F) Vegetative cells apical view. Scale bar 10 µm.

FIGURE 3. Scanning electron micrographs of the cells of Cosmarium hiranoi sp. nov. (A-C) from the Oasis Larsemann Hills (Antarctida) and C. clepsydra (D-F) (from Murmansk region). A, D) Vegetative cells frontal view; B, E) vegetative cells apical view; C, F) the cell wall structure (indicated by arrows). Scale bars: A, B, D, E—5 µm, C—1 µm, F—2 µm.