Pachysphaera Ostenfeld, 1899
Holotype species: Pachysphaera pelagica Ostenfeld
Original publication and holotype designation: Ostenfeld, C.H. (1900 '1899'). Plankton. In: Iagttagelsen over overfladevandets temperatur, saltholdighed og plankton paa islandske og grønlandske skibsrouter i 1899. (Knudsen, M. & Ostenfeld, C. Eds), pp. 45-93. Copenhagen: Bianco Lunos Kgl. Hof-Bogtrykkeri.
Request PDFDescription: Unicellular alga which occurs in 2 phases, a coccoid so-called Phycoma stage and a quadriflagellate motile stage. The Phycoma stage is spherical up to 175 µm in diameter. It is surrounded by a thick bilayered wall, the inner part of pectic material, the outer of material resembling sporopollenin. The outer wall is punctate, smooth or with various patterns. The young Phycoma measures ca 10 µm in diameter and contains a single nucleus, a chloroplast and a pyrenoid. It soon increases in diameter (as much as 5 µm per day), and the chloroplast divides into many small disc-shaped chloroplasts with globose pyrenoids. When the cyst has reached its final size, the contents divide into quadriflagellate cells, each with a parietal chloroplast with a pyrenoid but without eyespot. These cells emerge through a slit in the outer wall, still surrounded by the inner wall. Rupture of the inner wall releases the motile stage. The motile stage possesses 4 very long flagella (4-9 times cell length) which are held posteriorly during swimming. The flagella and cell body are covered by several types of scales. The motile stage divides by fission. The changeover from motile to Phycoma stage is apparently related to the lunar cycle. Sexual reproduction unknown.
Information contributed by: Ø. Moestrup. The most recent alteration to this page was made on 2014-09-22 by M.D. Guiry.
Taxonomic status: This name is of an entity that is currently accepted taxonomically.
Most recent taxonomic treatment adopted: Chrétiennot-Dinet, M.-J. (1990). Atlas du phytoplancton marin. Volume III: Chlorarachnophycées, Chlorophycées, Chrysophycées, Cryptophycées, Euglénophycées, Eustigmatophycées, Prasinophycées, Prymnesiophycées, Rhodophycées et Tribophycées Avec la collaboration de Chantal Billard et Alain Sournia. pp. [1]-261. Paris: Éditions du Centre National de la Recherche Scientifique 15, quai Anatole France - 75700 Paris.
Comments: The two described species differ in ornamentation of the wall of the Phycoma stage and in shape, flagellar insertion and length of the motile stage. At least 10 additional undescribed species were reported by Boalch and Parke (1971). The Phycoma stage is widely distributed in the plankton of Atlantic and undoubtedly also many other seas. Up to 200 Phycomas per litre have been recorded. The Phycoma is very similar to the microfossil Tasmanites. Pachysphaera is closely related to Pterosperma, but differs in the lack of wings in the Phycoma stage.
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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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Citing AlgaeBase
Cite this record as:
M.D. Guiry in Guiry, M.D. & Guiry, G.M. 22 September 2014. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. https://www.algaebase.org; searched on 22 November 2024
