Stephanosphaera Cohn, 1852

Holotype species: Stephanosphaera pluvialis Cohn

Original publication and holotype designation: Cohn, F. (1852). Über eine Gattung aus der Familie Volvocineen. Zeitschrift für wissenschaftliche Zoologie 4: 77–-116, pl. VI: figs 1-21.

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Description: Biflagellate vegetative cells uninucleate, aggregated into globose to slightly ellipsoidcolonies by a rather firm mucilage envelope 30-66 um wide. Coloniesusually of 8 cells, more rarely 2, 4, or 16 cells. Single celled stagesrare, resembling Haematococcus. Individual cells of colony 9-13 umwide and 9-35 um long, lack cellulosic cell walls and arranged equidistantlyand circumferentially within mucilage envelope with long axes parallel.In 16 celled colonies, cells arranged in two tiers of 8 cells each.Individual cells usually elongate-ellipsoid and distinctly inflated atmidregion, approaching a fusiform shape. Poles of each cellwith several cytoplasmic threads extending to inner surface of colonialenvelope; less distinct cytoplasmic threads may connect cells laterally.Chloroplast parietal, and cup shaped, often with extensions into basal regionsof apical cytoplasmic threads. Pyrenoid number variable, most commonly 2,one near each pole of the cell. Flagella usually twice as long as thecell, extending beyond mucilage envelope for some distance. Cells withnumerous irregularly distributed contractile vacuoles and a large stigma,located posterior to point of flagellar insertion.Asexualreproduction by division of cell into 4 or 8 daughter protoplasts that giverise to an autocolony that is released from the mother colony. Mucilage envelope of newly formed daughter colony initially not distinct.Aplanospores and akinetes may also be produced. Sexual reproductionisogamous, involving fusion of distinctly fusiform gametes, the quadriflagellate planozygote retaining motility for brief period. Mature zygotes globose, smooth-walled and typically red. Meiosis apparentlyzygotic, usually giving rise to 4 zoospores, each of which, after partitioning,gives rise to a vegetative colony.

Information contributed by: G.E. Dillard. The most recent alteration to this page was made on 2012-06-29 by Michael Guiry.

Taxonomic status: This name is of an entity that is currently accepted taxonomically.

Most recent taxonomic treatment adopted: Masjuk, N.P., Lilitska, G.G. & Kapustin, D.O. (2011). Chlamydomonadales. In: Algae of Ukraine: diversity, nomenclature, taxonomy, ecology and geography. Volume 3: Chlorophyta. (Tsarenko, P.M., Wasser, S.P. & Nevo, E. Eds), pp. 157-218. Ruggell: A.R.A. Gantner Verlag K.-G..

Comments: Stephanosphaera is a rare freshwater alga infrequently reported fromEurope and the United States

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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.

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Michael Guiry in Guiry, M.D. & Guiry, G.M. 29 June 2012. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway.; searched on 23 July 2024

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