Mychonastes koreanus H. Lee, T. Kim, & J. Ki 2025, sp. nov.

Mychonastes koreanus H. Lee, T. Kim, & J. Ki sp. nov. (Fig. 2A–E) Description: Cells are green to light yellowish-green, single, planktonic, and spherical. Cell wall is sculptured in SEM observation. They are 1.5 to 3.5 μm in diameter, with an average of 2.75 μm. They lack a mucilaginous envelope and stalks. They do not form colonies, except during propagation two or four autospores after sporulation remain attached for a short time. The chloroplast is single, parietal, and cup-shaped without pyrenoids. This species is distinguished from other Mychonastes species by the nucleotide composition of the rRNA ITS2 sequence and its secondary structure. Etymology: The name of the country (Korea) where the species was discovered was reflected. Holotype: A permanent microscopic slide, NIBRCL0000117313 in the Herbarium at the National Institute of Biological Resources, from cultured strain SMU-GA001. Type locality: Yun-gang River, Toegang-ri, Sabeolguk-myeon, Sangju-si, Gyeongsangbuk-do, Korea (36°31'36.3"N, 128°15'50.5"E). Distribution: To date, Mychonastes koreanus has only been observed in this type of locality. At the time of collection, the pH was 8.0, and the water temperature was 17.1 °C. Gene sequences: partial 18S rRNA, ITS1, 5.8S, ITS2, and partial 28S rRNA gene sequences with GenBank accession number OR914224.