Mychodea pusilla (Harv.) J.Agardh

Scientific Description

Habit and structure. Thallus red-brown, tufted, 1–3(–4) cm high, subdichotomously to irregularly branched often with numerous short laterals, branches terete, 200–500 µm in diameter. Holdfast discoid, 200–600 µm across, epiphytic on the stems of Amphibolis. Structure uniaxial, with a prominent apical cell and axial filament at least in younger parts, with a filamentous inner medulla, large-celled outer medulla, and small-celled cortex, outer cells ovoid, 3–4 µm in diameter. Rhodoplasts discoid to elongate, ribbon like in inner cells.

Reproduction. Sexual thalli monoecious; procarpic; polycarpogonial. Carpogonial branches 3-celled, 2–4 borne on enlarged inner cortical cells, with the auxiliary cell producing gonimoblast filaments (mainly thallus-inwardly) which cut off clusters of ovoid carposporangia 10–22 µm in diameter within the filamentous matrix. Cystocarps 1–3 in lesser branchlets, swollen, 0.6–1 mm in diameter, with spinous tips; enveloping tissue slight, cortex normal. Spermatangial clusters scattered, sunken in the outer cortex, with 4–6 initials each bearing 2 elongate-ovoid spermatangia 1.5–2.5 µm in diameter. Tetrasporangia scattered in the outer cortex, laterally attached, ovoid, 30–50 µm long and 15–30 µm in diameter, zonately divided.

Distribution:Port Denison, W. Aust., to Walkerville, Vic.

Habitat. M. pusilla is restricted to the stems of Amphibolis from low tide level to 12 m deep, under moderate to strong water movement. 

[After Womersley, Mar. Benthic Fl. Southern Australia IIIA: 464 (1994)]