Habit and structure. Thallus light to medium red, foliose, 3–7 cm high and 3–6 cm across, gradually to broadly cuneate from a short stipe, with the rounded upper margin becoming irregularly lobed; margin and usually the surface (except basal part) densely covered with short, branched spines 1–2 mm long; thallus fairly firm, adherent to paper. Holdfast discoid, 1–2 mm across; epilithic. Structure. Thallus 200–350 µm thick, consisting of 3–4 layers of cortical cells and a central medulla of dense, slender filaments 2–5(–8) µm thick, often lying parallel to the surface in young parts but denser and with many filaments crossing the medulla in older parts; large, darkly staining refractive cells with long arms are common and prominent in the medulla, occasionally remaining joined as a partial network; outer cortical cells compact, in surface view isodiametric to elongate and 7–11 µm across, isodiametric in sectional view of thallus.
Reproduction. Carpogonial branch systems monocarpogonial with the mature supporting cell broader at its upper end and bearing 2(–3) elongate, slightly clavate subsidiary cells and a carpogonial branch with first and second cells elongate. Auxiliary cell systems relatively small (about 20 µm across), consisting of a subspherical auxiliary cell and three subsidiary cells. Post-fertilization stages and cystocarps not observed. Male plants unknown. Tetrasporangia scattered over the thallus in the cortex, 30–38 µm long and 20–26µm in diameter, cruciately divided.
Distribution. Known from the type and Pearson I., S. Aust., 22 m deep, and from St Francis I., Isles of St Francis, S. Aust., 55 m deep.
[After Womersley, Mar. Benthic Fl. Southern Australia IIIA: 238–239 (1994)]