Nemacystus decipiens (Suringar) Kuck.

Scientific Description

Habit and structure. Thalli epiphytic on various hosts, especially Sargassum spp. and, occasionally, Hydroclathrus. Thalli usually golden brown to dark brown, 2.0–4.5 cm long; juveniles epiphytic on Cladophora goweri as small as 4 mm long. Branching sparingly subdichotomous and irregularly radial. Main axes beset with varying numbers of short patent laterals that in some specimens are rather regularly 3–5 mm apart; lower main axes to 800 µm in diameter, those above 250–500 µm in diameter. Apices of axes densely clothed in upwardly directed cortical filaments and interspersed trichothallic hairs. Apical cells of the central axes generally obscured by surrounding filaments, but dissection shows them to be domed and cutting off derivatives by an almost transverse division. Although the central axial filament is not visible in mature cross-sections, in narrow laterals it can sometimes be seen as a continuous row of narrow elongate cells surrounded by the outer medulla. Central medullary cells thin-walled, pseudoparenchymatous, 100–500 µm long, 50–130 µm in diameter, grading to a mixture of smaller cells (10–50 µm in diameter) peripherally. Unbranched assimilative filaments arising perpendicularly on each of the peripheral medullary cells, 11–15 cells and 150–250 µlm long, arching distally toward the apex of the bearing axis, consisting distally of deeply pigmented ovoid to submoniliform cells 10–25 x 10–13 µm and proximally of several narrower rectilinear cells. Trichothallic hairs sparse to very numerous from lower cells of assimilators, to 1200 µm long, increasing the axis diameter to almost 3 mm.

Reproduction. Plurangia forming in digitate stalked fascicles 30–50 µm long borne on basal cells of assimilative filaments, simple or subdichotomous, divided uniseriately by transverse and oblique cross-walls, 3–5 µm wide. Unangia uncommon in Lord Howe Island material, ovoid to slightly clavate, 40–50 µm long and 15–20 µm wide, sessile on inner cortical cells.

Distribution. Occurs in the Indian Ocean (Mauritius, Bahrain, Kuwait, Saudi Arabia, Pakistan and India), Japan, China, Korea, the Hawaiian Islands, Qld. and Lord Howe I.

[After Kraft, Algae of Australia: Marine Benthic Algae of Lord Howe Island and the Southern Great Barrier Reef, 2: Brown Algae:85–86 (2009)]