Antithamnionella graeffei (Grunow) Athanas.

Scientific Description

Habit and structure. Thallus pale red, with prostrate axes spreading to several millimetres, bearing erect axes to 2 mm tall. Erect axes with 3 whorl branches per axial cell. Lateral branches arising from basal cells of the whorl branches. Cells of primary axes to 30 µm diam. [L:B c. 5]. Whorl branches with the basal cell shorter than distal cells and unbranched, otherwise pseudodichotomously branched in mid-branch and unbranched distally; cells 7.5–10.0 µm diam. near the base, tapering to 4–5 µm diam. near the apex [L:B c. 5]. Vesicular cells ellipsoidal, formed laterally on cells of whorl branches, not in series, to 10 µm long.

Reproduction. Spermatangia formed in heads on whorl branches, composed of a series of 3–5 spermatangial mother cells, each bearing 2 or 3 lateral spermatangia. Spermatangial heads solitary or in clusters of up to 3 per bearing cell. Procarps terminal. Mature cystocarps with 3 or 4 gonimolobes to 50 × 35 µm, composed entirely of carposporangia c. 15 µm diam. Tetrasporangia sessile on basal cells of whorl branches, solitary or accompanied by a younger sporangium, ellipsoidal, 40–50 × 30–35 µm, cruciately or decussately divided.

Distribution. Widespread in tropical and warm-temperate seas. In Australia known from the Great Barrier Reef and in north-western Australia from the Montebello Islands north to Cassini Island.

Habitat. Epiphytic or epizoic in the subtidal.

[After J.M. Huisman in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 374–375 (2018)]