Sonderophycus fervens K.R.Dixon

Scientific Description

Habit and structure. Thallus partially encrusting, often on sponges or ascidians, but with free margins, deep red to pink or mottled red and yellow, usually with distinct radial striae. Blades cartilaginous and broadly lobed, spreading to 2–3 cm in width. Dorsal surface with clusters of cystoliths visible under low magnification. Blades 100–330 μm and 6–21 cell layers thick, composed of a monostromatic hypothallus and a thick weakly calcified dorsal perithallus. Hypothallus composed of parallel radiating filaments of elongate cells 23–50 μm long and 4–10 μm diam. Perithallial filaments arising at narrow angles to the hypothallus (<45°), straightening to become ±vertical at the thallus surface, 6–15 μm diam., composed of elongate [L:B 3–7] cells below, these becoming shorter above [L:B to 1]. Zones of secondary perithallial growth frequent distally. Horizontally directed filaments occasional, sometimes copious among the lower assurgent perithallial filaments. Calcification present as clustered cell wall thickenings (cystoliths) in the middle to upper perithallus and as a thin external hypobasal layer among the rhizoids. Rhizoids multicellular, 8–10 μm diam., composed of unbranched filaments of long slender cells attached to the lower distal faces of hypothallial cells by a rhizoidal coxal cell that is bent upon emergence from the lower cuticle.

Reproduction. Tetrasporangia small, 45–65 μm long and 10–20 μm diam., cruciately divided, borne on small cupulate unicellular pedicels among simple robust paraphyses in raised subcircular gelatinous nemathecia scattered on the thallus surface. Gametophytic reproduction not seen.

Distribution. Widespread in the tropical Indo-Pacific region.

[After K.R. Dixon in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 242–244 (2018)]