Myrionema strangulans Greville
Description: Greenish-brown to medium brown, regularly discoid, 0.5–2 (–5) mm across, epiphytic on Ulva, discs often merging. Basal layer monostromatic, of subdichotomous, radiating, closely adjacent filaments adherent to the host surface, with marginal cells more elongate and inner cells mostly 8–14 µm long, 5–8 µm broad and 4–8 µm high. Erect assimilatory filaments forming a shallow even dome, arising from almost every cell of the basal layer commencing 10–20 cells within the disc margin, when mature 100–130 and 5–8 cells high, with the cells 15–25 µm long and 4–6 µm in diameter, with the terminal cell slightly clavate, 10–25 µm long and 7–10 µm in diameter; cells with several discoid to irregularly-shaped phaeoplasts, each with 1 (–2) pyrenoids. Hairs scattered, 8–12 in diameter.
Habitat: Epiphytic on older plants of Ulva species, particularly distromatic types.
Key characteristics: Small brown discs.