Urospora Areschoug, 1866, nom. cons.
Holotype species: Urospora mirabilis Areschoug
Currently accepted name for the type species: Urospora penicilliformis (Roth) Areschoug
Original publication and holotype designation: Areschoug, J.E. (1866). Observationes phycologicae. Particula prima. De Confervaceis nonnullis. Nova Acta Regiae Societatis Scientiarum Upsaliensis, Series 3 6(2): 1-26, 4 pls. [in Latin]
Description: Plants consisting of slender to course, unbranched, uniseriate filaments, rarely over 10 cm long, attached by external descending rhizoids from lower several cells. Mature vegetative cells multinucleate. Cell walls microfibrillar, and 2-layered, outermost electron-dense, covered by thin gelatinous layer. Chloroplast in young cells an open girdle, when mature with many perforations, covering entire inner wall, including crosswalls. Pyrenoids surrounded by numerous starch grains and penetrated by tubular chloroplast stroma invaginations as in all Acrosiphoniales. No plasmodesmata observed. Asexual reproduction of gametophytes by acuminate, quadriflagellate zoospores and occasionally by aplanospores and akinetes formed in ordinary cells. Exit apertures of sporangia little differentiated. Zooids enclosed within a vesicle retained or released from zooidangia, when internal separated from cell wall by abscission zone. Zoospores similar to those produced by sporophyte, with one chloroplast containing one pyrenoid and double layered, indistinct stigma. Flagellar apparatus with four flagella inserted apically in cavities of cruciform papillae, each flagellum bearing proximally undulating wings projecting from peripheral microtubules of flagellar axoneme. Basal bodies cruciately arranged, non-overlapping, associated with striated fibrous complex and two rhizoplasts. Microtubular roots consistently nine in Urospora penicilliformis. Transverse lamellae in transition region of basal bodies, the latter without stellate or cartwheel patterns. Life history haplodiplontic and heteromorphic with alternation of filamentous gametophyte and Codiolum-like sporophyte. Sexual reproduction anisogamous with biflagellate gametes produced by unisexual filaments. Male gametes ovoid to irregularly spindle-shaped, fast swimming with poorly developed chloroplast, inconspicuous stigma and no pyrenoid. X-rootlets lacking, terminal cap simple, the proximal sheath a single large unit. Proximal ends of basal bodies overlapping, arranged in a 11/5 o'clock configuration. Neither body nor flagellar scales present. Female gametes ovoid-elliptical, larger and slower than males, with one chloroplast and pyrenoid and distinct eyespot. Flagellar apparatus with cruciately arranged rootlets (X=3?). Zygotes developing into stalked, generally free-living epilithic Codiolum-stage producing quadriflagellate, acuminate, probably meiotic, zoospores on maturity. Parthenogenetic development of gametes into Codiolum-phase possible. Aplanospores in stalkless sporophytes developed from female gametes in U. penicilliformis. Some species seem to have lost their sexual reproduction, whereas others have geographical sexual strains. Urospora mostly distributed in cold temperate waters of both hemispheres, and also in arctic and antarctic seas growing on hard substrata in the middle-upper intertidal zone and the splash zone. All cells in Urospora filament, except basal cells, undergo division. Cell division in a four- day rhythm, restricted to active region, differing from day to day, and generally proceeding in mature plants downward to base. Mitosis and cytokinesis involving considerable cell elongation and formation of hyaline cytoplasmic equatorial band into which nuclei migrate and undergo synchronous divisions. Two bands of daughter nuclei move away from one another during ingrowth of cleavage furrow. Non-migrating nuclei also divide. "Free" divisions of nuclei may also occur in not fully elongated cells without cytokinesis. During mitosis centrioles become apparent. Nuclear envelope partially broken down or maintained except for polar gaps. Numerous microtubules connect chromosomes and poles, but kinetochores apparently absent. Centrioles take lateral position near spindle poles. In anaphase, chromosomes migrate simultaneously towards opposite poles and a cylindrical interzonal spindle develops between the chromosome sets which later disappears. The ingrowing annular septum is preceded by a hoop of cytokinetic microtubules.Diffraction pattern of cell walls indicates mercerized cellulose with randomly arranged microfibrils. The neutral wall polysaccharides composed of galactose, glucose, mannose, xylose and rhamnose, the latter two being most abundant; polysaccharides of sporophytes differ from gametophytes by their high concentration of mannose; special dwarf plants mainly with glucose in cell wall. Experiments based on 14CO2 incorporation revealed temperature correlated differences in metabolism between filamentous plants (50C), Codiolum-plants (ca. 100C) and dwarf plants (ca. 140C), suggesting temperature-sensitive differential gene expression and/or metabolic steps.
Information contributed by: S. Jónsson. The most recent alteration to this page was made on 2015-10-19 by M.D. Guiry.
Taxonomic status: This name is of an entity that is currently accepted taxonomically.
Gender: This genus name is currently treated as feminine.
Most recent taxonomic treatment adopted: Lindstrom, S.C. & Hanic, L.A. (2005). The phylogeny of North American Urospora (Ulotrichales, Chlorophyta) based on sequence analysis of nuclear ribosomal genes, introns and spacers. Phycologia 44: 194-201.
Comments: According to Lindstrom & Hanic (2005), the uninucleate genus Chlorothrix rather than the multinucleate Acrosiphonia is the genus closest to Urospora.
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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.
Linking to this page: https://www.algaebase.org/search/genus/detail/?genus_id=32819
Cite this record as:
M.D. Guiry in Guiry, M.D. & Guiry, G.M. 19 October 2015. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. https://www.algaebase.org; searched on 31 January 2023