Electronic Flora of South Australia Species Fact Sheet

Mychodea pusilla (Harvey) J. Agardh 1872: 34; 1876: 571; 1897: 50.

Phylum Rhodophyta – Class Florideophyceae – Order Gigartinales – Family Mychodeaceae

Selected citations: Kraft 1978: 533, figs 7–9, 33, 34. Kylin 1932: 64. Lucas & Perrin 1947: 156.

Synonyms

Dicranema pusilla Harvey 1855a: 550.

Acanthococcus pusillus (Harvey) Harvey 1863: pl. 266.

Hypnea fastigiata Harvey 1863, synop.: xxxvi.

Mychodea fastigiata (Harvey) J. Agardh 1872: 34; 1876: 572; 1897: 51. Kylin 1932: 64, pl. 26 fig. 65. Lucas & Perrin 1947: 156.

Thallus (Fig. 163D, E) red-brown, tufted, 1–3 (–4) cm high, subdichotomously to irregularly branched often with numerous short laterals, branches terete, 200–500 µm in diameter. Holdfast discoid, 200–600 µm across, epiphytic on the stems of Amphibolis. Structure uniaxial, with a prominent apical cell and axial filament at least in younger parts, with a filamentous inner medulla, large-celled outer medulla (Fig. 165B), and small-celled cortex, outer cells ovoid, 3–4 µm in diameter. Rhodoplasts discoid to elongate, ribbon like in inner cells.

Reproduction: Sexual thalli monoecious; procarpic; polycarpogonial. Carpogonial branches (Fig. 165C) 3-celled, 2–4 borne on enlarged inner cortical cells, with the auxiliary cell (Fig. 165D) producing gonimoblast filaments (mainly thallus-inwardly) which cut off clusters of ovoid carposporangia 10–22 µm in diameter within the filamentous matrix. Cystocarps (Fig. 165A) 1–3 in lesser branchlets, swollen, 0.6–1 mm in diameter, with spinous tips; enveloping tissue slight, cortex normal. Spermatangial clusters (Fig. 165E) scattered, sunken in the outer cortex, with 4–6 initials each bearing 2 elongate-ovoid spermatangia 1.5–2.5 µm in diameter.

Tetrasporangia (Fig. 165F) scattered in the outer cortex, laterally attached, ovoid, 30–50 µm long and 15–30 µm in diameter, zonately divided.

Type from King George Sound, W. Aust. (Harvey, 1854); lectotype in Herb. Harvey, TCD (Tray. Set No. 80).

Selected specimens: (all on Amphibolis): Port Denison, W. Aust., drift (Kraft, 14.xii.1971; AD, A44702). Cape Leeuwin, W. Aust., drift (Kraft, 12.xii.1971; AD, A44703). Eucla, W. Aust., drift (Womersley, 2.ii.1954; AD, A19372). Petrel Bay, St Francis I., Isles of St Francis, S. Aust., 2 m deep (Shepherd, 10.i.1971; AD, A38409). Tiparra Reef, S. Aust., 5 m deep (Shepherd, 20.viii.1971; AD, A39461). D'Estrees Bay, Kangaroo I., S. Aust., outer reef pool (Womersley, 11.i.1950; AD, Al2696). Port Elliot, S. Aust., drift (Womersley, 17.x.1948; AD, A9398). Robe, S. Aust., 0.5 m deep near jetty (Kraft, 10.ii.1973; AD, A44705). Queenscliff, Vic., drift (Womersley, 8.iv.1959; AD, A22849). Western Port, Vic., 3–4 m deep on Amphibolis (Kraft & Saunders, 9.i.1992; MELU, K8757). Walkerville, Vic., drift (Sinkora A2104, 27.ii.1975; AD, A48407).

Distribution map based
on current data relating to
specimens held in the
State Herbarium of SA

Distribution: Port Denison, W. Aust., to Walkerville, Vic.

Taxonomic notes: M. pusilla is the smallest species of Mychodea and is restricted to the stems of Amphibolis from low tide level to 12 m deep, under moderate to strong water movement. It is characterised also by the terete radial branches and position of the cystocarps.

References:

AGARDH, J.G. (1872). Bidrag till Florideernes Systematik. Acta Univ. hind. 8, 1–60.

AGARDH, J.G. (1876). Species Genera et Ordines Algarum. Vol. 3, Part 1 - Epicrisis systematis Floridearum, pp. i-vii, 1–724. (Weigel: Leipzig.)

AGARDH, J.G. (1897). Analecta Algologica. Cont. IV. Acta Univ. lund. 33, 1–106, Plates 1, 2.

HARVEY, W.H. (1855a). Some account of the marine botany of the colony of Western Australia. Trans. R. Ir. Acad. 22, 525–566.

HARVEY, W.H. (1863). Phycologia Australica. Vol. 5, Plates 241–300, synop., pp. i-lxxiii. (Reeve: London.)

KRAFT, G.T. (1978). Studies of marine algae in the lesser-known families of the Gigartinales (Rhodophyta). III. The Mychodeaceae and Mychodeophyllaceae. Aust. J. Bot. 26, 515–610.

KYLIN, H. (1932). Die Florideenordnung Gigartinales. Lunds Univ. Årsskr. N.F. Avd. 2, 28 (8), 1–88, Plates 1–28.

LUCAS, A.H.S. & PERRIN, F. (1947). The Seaweeds of South Australia. Part 2. The Red Seaweeds. (Govt Printer: Adelaide.)

The Marine Benthic Flora of Southern Australia Part IIIA complete list of references.

Author: G.T. Kraft & H.B.S. Womersley

Publication: Womersley, H.B.S. (14 January, 1994)
The Marine Benthic Flora of Southern Australia
Rhodophyta. Part IIIA, Bangiophyceae and Florideophyceae (to Gigartinales)
Reproduced with permission from The Marine Benthic Flora of Southern Australia Part IIIA 1994, by H.B.S. Womersley. Australian Biological Resources Study, Canberra. Copyright Commonwealth of Australia.

Illustrations in Womersley Part IIIA, 1994: FIGS 163D, E, 165 A–F.

Figure 163   enlarge

Fig. 163. A. Mychodea spinulifera (AD, A34186). Habit, on Amphibolis. B, C. Mychodea aciculare (B, AD, A44712; C, AD, A44711). B. Habit. C. Cross section of cystocarp with emergence of the hydrozoan on the right. D, E. Mychodea pusilla (D, lectotype in TCD; E, AD, A44703). D. Habit. E. Habit of a cystocarpic plant. F, G. Mychodea acanthymenia (AD, A44728). F. Habit of holotype. G. Section of a mature cystocarp. [D–G as in Kraft 1978.]

Figure 165   enlarge

Fig. 165. A–F. Mychodea pusilla (AD, A44705). A. Branches with cystocarps. B. Transverse section of a branch with tetrasporangia. C. Section of cortex with polycarpogonial supporting cells. D. Section of cortex with an auxiliary cell producing gonimoblast initials. E. Section of cortex with a sunken spermatangial cluster. F. Section of cortex with tetrasporangia. G–K. Mychodea acanthymenia (AD, A44728). G. Upper branches with spinous ramuli (cystocarpic on left). H. Transverse section of branch. I. Section of cortex with polycarpogonial supporting cells. J. Section of cortex with sunken spermatangial clusters. K. Longitudinal section of thallus with tetrasporangia. [A–K after Kraft 1978.]

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