Cryptocallis dixoniorum Huisman & G.W.Saunders

Scientific Description

Habit and structure. Thallus prostrate, deep red to mottled, spreading to 18 cm, with a discoid holdfast and several secondary attachments, irregularly branched. Blades flattened, cartilaginous, 600–800 µm thick. Structure multiaxial, with a filamentous medulla 150–200 µm thick, of elongate cylindrical cells 5–10 µm diam., these mostly longitudinally aligned but occasionally with transverse filaments traversing between opposite outer medullary cells. Outer medulla with 3 or 4 layers of ellipsoidal, ovoid or subspherical cells, the innermost 85–120 µm diam., outer with progressively smaller cells, then grading to a 3- or 4-layered cortex of pigmented cells. Cortical cells spherical to anticlinally elongate, the surface cells 3–5 µm diam., those of the ventral thallus surface generally larger and more spherical.

Reproduction. Gonimoblast initial with numerous small satellite cells. Fusion cell formed by broadening of the pit connection between auxiliary cell and gonimoblast initial. Cystocarps grouped in raised nemathecia formed by extension of subcortical cells, the cortex remaining as an outer layer. Tetrasporangial nemathecia circular to irregular in shape, 2–12 mm wide. Tetrasporangia terminal or lateral on branched filaments, elongate when immature, becoming ellipsoidal or obovoid, 40–50 µm long, 20–25 µm diam., irregularly cruciate, often appearing zonate due to realignment of spores. Tetraspores each with a prominent central nucleus.

Distribution. Known from the Kimberley coast of north-western Australia and the northern Philippines.

Habitat. Epilithic in the subtidal, typically on deeply undercut vertical reef walls in shaded positions.

[After J.M. Huisman & G.W. Saunders in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 300 (2018)]