Astrephomene M.A.Pocock, 1954: 109
Classification:
Empire Eukaryota
Kingdom Plantae
Subkingdom Viridaeplantae
Phylum Chlorophyta
Class Chlorophyceae
Order Volvocales
Family Goniaceae
Holotype species: Astrephomene gubernaculifera M.A.Pocock
Taxonomic status: currently recognized as a distinct genus.
Description: Colonies ovoid or subspherical, containing 32, 64 or 128 cells arranged radially at the periphery of a gelatinous matrix. Colonies with two to several small somatic cells (rudder cells) at posterior pole. Cells nearly spherical or lenticular, each with two equal flagella, a stigma, many contractile vacuoles on the surface and a massive cup-shaped chloroplast that lacks pyrenoids or develops one in the brim. Stigmata in anterior cells larger than in posterior cells. Each protoplast enclosed by a gelatinous sheath and constitutive cells attach or connect by the fusion or attachment or these sheaths, forming a hollow colony. Asexual reproduction by autocolony formation, each reproductive cell of the colony dividing successively to form a daughter colony without inversion. In sexual reproduction, each reproductive cell of the colony escapes from the gelatinous matrix to become an isogamete, and walled aplanozygotes are formed. On germination, the zygote gives rise to a single biflagellate gone cell.
Comments: Astrephomene is rare and grows in freshwater rich in organic matter. Astrephomene was described with a single species, A. gubernaculifera. It was referred to a new family because colony formation lacked the inversion characteristic of Volvocaceae. A. perforata was later described from Japan. The two species differ in characters of the gelatinous cellular sheaths, pyrenoids and number of somatic cells. A close phylogenetic relationship was suggested between Astrephomene and Gonium, based on sensitivity of the gelatinous matrix to an enzyme and on ultrastructure of the matrix. Sexual isolation shown in groups of A. gubernaculifera from USA and Mexico with chromosome numbers of four, seven or eight. Effects of vitamins, carbon sources, pH and temperature on growth investigated in A. gubernaculifera. DNA isolated, partially purified and characterized for this species. Ultrastructure of cell division and flagellar apparatus examined. Astrephomene may have evolved from ancestors that invert.
NCBI Nucleotide Sequences
Numbers of names and species: There are 2 species (and infraspecific) names in the database at present, of which 2 have been flagged as currently accepted taxonomically.
Names: ('C' indicates a name that is currently accepted taxonomically; 'S' a homotypic or heterotypic synonym; 'U' indicates a name of uncertain taxonomic status, but which has been subjected to some verification nomenclaturally; 'P' indicates a preliminary AlgaeBase entry that has not been subjected to any kind of verification. For more information on a species click on it to activate a link to the Species database):
Astrephomene gubernaculifera M.A.Pocock C - type
Astrephomene perforata Nozaki C
Information contributed by: H. Nozaki. The most recent alteration to this page was made on 27 Mar 2010 by M.D. Guiry.
Contributors
Some of the descriptions included in AlgaeBase were originally from the unpublished Encyclopedia of Algal Genera,
organised in the 1990s by Dr Bruce Parker on behalf of the Phycological Society of America (PSA)
and intended to be published in CD format.
These AlgaeBase descriptions are now being continually updated, and each current contributor is identified above.
The PSA and AlgaeBase warmly acknowledge the generosity of all past and present contributors and particularly the work of Dr Parker.
Descriptions of chrysophyte genera were subsequently published in J. Kristiansen & H.R. Preisig (eds.). 2001. Encyclopedia of Chrysophyte Genera. Bibliotheca Phycologica 110: 1-260.
