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ORDER ACROSIPHONIALES Jonsson

Phylum Chlorophyta

Thallus (gametophyte) simple or branched, slender to robust, filaments uniseriate. Cells usually multinucleate (uninucleate in Spongomorpha) with nuclear division occurring in the plane of cross wall formation prior to ingrowth of the cross wall from the periphery; chloroplast single, parietal, continuous but perforate, containing several to many polypyramidal pyrenoids; cell wall without cellulose I but with mannan, xylan and pectic substances (fibrils similar to cellulose II also suggested). Sporophyte (Codiolum stage) minute, unicellular, ovoid with a basal rhizoid.

Reproduction: Reproduction by biflagellate iso- or anisogametes or biflagellate zoospores from the gametophytes, developed in almost any thallus cell, liberated through an operculate pore (at least in Acrosiphonia), and by quadriflagellate meiospores from the unicellular sporophyte; or parthenogenetic from either phase.

Life history diplohaplontic and heteromorphic, or haplontic (see Tanner 1981, p. 229).

Taxonomic notes: The order Acrosphoniales is separated from the Cladophorales by most recent authors, but the features considered characteristic of the order have been established in only a few species, and their general application remains to be verified. Several of these features are at a subcellular or ultrastructural level (e.g. wall structure) and not easy to detect, but the chloroplast form and nature of the pyrenoids, the operculate pores to the zooidangia, and the heteromorphic life history are the more readily observable (Jonsson 1962, p. 199; van den Hoek 1963, pp. 20–22). However, the presence of operculate pores appears not to have been established for Urospora, where illustrations show only simple pores.

References:

JONSSON, S. (1962). Sur la reproduction de l'Anadyomene stellata (Wulf) Ag. de la Méditerranee. C.R. Acad. Sci. Paris. 255, 1983–1985.

TANNER, C.E. (1981). Chlorophyta: Life histories. In Lobban, C.S. & Wynne, M. J. (Eds), The Biology of Seaweeds, Ch 6, pp. 218–247. Botanical Monogr. Vol. 17. (Blackwell: Oxford.)

VAN DEN HOEK, C. (1963). Revision of the European species of Cladophora. (Brill: Leiden.)

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

Author: H.B.S. Womersley

Publication: Womersley, H.B.S. (31 May, 1984)
The Marine Benthic Flora of Southern Australia
Part I
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