Erythrotrichia bohanensis Huang, Chu & Ding 2025, sp. nov.

Erythrotrichia bohanensis Huang, Chu & Ding sp. nov. Description. Thallus rose-red, green to purple in color, with erect, mostly unbranched filaments. The thallus consists of a uniseriate row of cells. Mature thalli reach a height of 4.7–5.2 mm. The base of the thallus is discoid in shape (Fig. 3 C), that facilitates attachment to the host algal surface (Fig. 3 A, B). The diameter of the attachment disc ranges from 41.0 to 60.8 μm (Fig. 3 C, H). The thallus tapers from bottom to top, with the diameter 19.5–22.7 μm at the base, 17.2–18.10 μm in the middle, and 9.7–11.4 μm in the upper part. Vegetative cells are elongate-ovoid in shape, with basal cells 13.2–16.0 μm in height and 8.2–11.9 μm in width, central cells 13.9–20.0 μm in height and 12.3–13.3 μm in width, and distal cells 15.0–17.6 μm in height and 7.2–8.0 μm in width. Apical cells are suborbicular, with a diameter of 8.3–8.5 μm. Cells are enveloped by a gelatinous membrane that lies external to the cell wall, 1–4 μm in thick (Fig. 3 D). Asexual reproduction occurs through monospores. Monosporangia are formed by vegetative cells dividing obliquely or longitudinally (Fig. 3 E), and one of these cells is transformed into a monosporangium releasing monospores, measuring 11.5–15 μm in diameter (Fig. 3 F, G). The monospores germinate into sporelings (Fig. 3 F – H). During monospore germination, the cell undergoes polar division, extending on one side to form a uniseriate filament and on the other side to form a unicellular disk (Fig. 3 F) or a polar pseudoroot with an expanding adhesive rhizoid tip (Fig. 3 G). In sexual reproduction, carpogonia are formed by the expansion and division of vegetative cells (Fig. 3 I), 17.0–22.0 μm in diameter. Spermatangia are derived from vegetative cells, exhibiting a lighter pigmentation compared to the latter. Spermatia are released after maturation in the male gametophyte (Fig. 3 J) or outside the thallus (Fig. 3 K). Colorless spermatia contact and fuse with carpogonia outside the thallus. Following fertilization the zygotes germinate into sporelings (Fig. 3 L). Holotype. TNU 20230511041 b, epiphyte on Polysiphonia morrowii Harvey. Type locality. Dongshan Beach, Qinhuangdao, Hebei Province, China (39°54'N, 119°37'E). Isotypes. TNU 20230318010 a epiphyte on Polysiphonia senticulosa Harvey, and TNU 20230511041 c, TNU 20230511041 d epiphyte on Polysiphonia morrowii Harvey. All specimens were preserved in the algae Laboratory, Tianjin Normal University, Tianjin, China. Etymology. Bohanensis, the holotype was collected from the Bohai Sea. DNA sequences. To be uploaded into Genbank. Distribution and habitat. Qinhuangdao, Hebei Province, China. Japan, Australia, America, the Netherlands, and South Africa. Epiphytic life, on macroalgae.