Gibsmithia indopacifica D.Gabriel, Draisma & Fredericq

Scientific Description

Habit and structure. Thallus to 6 cm tall, red, with a firm cartilaginous stalk bearing lobed or digitate mucilaginous branches with an outer covering of emergent filaments, these often retaining fine sand grains so that the thallus appears dusted. Primary filaments of mucilaginous branches with cylindrical cells 12–18 µm diam. [L:B c. 6]; cells of distal filaments becoming shorter distally, variable in shape, either subclavate or cylindrical. Slender rhizoidal filaments also common.

Reproduction. Spermatangia in determinate terminal or lateral heads on emergent filaments, these 3–5 cells long and bearing numerous spermatangial mother cells that bear spermatangia directly or additional mother cells. Carpogonial branches 7–10-celled, straight, with the distal cells spherical and enlarged; subhypogynous cell smaller than adjacent cells and the carpogonum slightly lateral on the hypogynous cell. Lower cells of carpogonial branches with unbranched sterile laterals. Postfertilisation and carposporophytes not observed. Tetrasporangia arising terminally or laterally on lateral filaments, subspherical to ellipsoidal, 17–22 µm long, 14–20 µm diam., mostly decussately divided, rarely cruciate.

Distribution. Widespread in tropical waters of the Indo-West Pacific.

Habitat. Epilithic in the subtidal.

[After J.M. Huisman in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 179 (2018)]