Thalassiosira Cleve, 1873

Holotype species: Thalassiosira nordenskioeldii Cleve

Original publication and holotype designation: Cleve, P.T. (1873). On diatoms from the Arctic Sea. Bihang till Kongliga Svenska Vetenskaps-Akademiens Handlingar 1(13): 1-28, 4 pl.

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Description: Cells discoid to cylindrical, solitary, or joined by threads or valve to valve to form loose chains; or in mucilage masses. Plastids numerous, discoid. Mainly in the marine plankton. Valve circular, with a flat valve face and short downturned mantles or sometimes almost watchglass-like. Areolae usually loculate, arranged in radial rows, tangential rows, or arcs; varying in size and prominence. The areolae open to the outside by circular foramina, sometimes with finger-like projections (e.g. T. ferrelineata); internally they are occluded by slightly raised cribra. Valve mantle edge often very prominently ribbed and rimmed. Fultoportulae are present in a ring around the valve mantle opening externally by short tubes; in some species scattered or grouped fultoportulae occur also on the valve face. The internal fultoportula structure varies; very short to very long tubes are surrounded by (3 or) 4 buttresses. Each valve usually has one rimoportula, which opens externally through a larger and more obvious tube, located somewhat internal to the marginal ring of fultoportulae; in some cases, however, the external tube can be thin and located close to fultoportulae (e.g. T. conferta); in a few species a rimoportula may occur in the centre of the valve face. The internal rimoportula opening is usually elongate and sessile. The mangle edge may be thickened internally in some species. Copulae numerous, split and ligulate. The valvocopula is more obviously areolate than the other copulae, with a loculation similar to that of the valve and a more conspicuous row of areolae adjacent to the valve mantle. A slight septum occurs on the valvocopula of T. trifulta which also has a complex triradiate ligula

The most recent alteration to this page was made on 2022-08-20 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: Stoermer, E.F. & Julius, M.L. (2003). Centric Diatoms. In: Freshwater Algae of North America. (Wehr, J.D. & Sheath, R.G. Eds), pp. 559-594. San Diego: Academic Press.

Comments: This is a large genus - descriptions of species (many new) are to be found in the numerous papers of Hasle & Fryxell. Most species (c. 100) are marine, although up to 12 have been recorded in freshwaters (Hasle, 1978); of the latter T. weissflogii (=T. fluviatilis) is probably the best known. There is considerable variation within the genus, which is one of the largest in our collection; we cannot do justice to it in our illustrations. Makarova (1988) provides a comprehensive account of the genus in seas around Russia.

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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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Cite this record as:
M.D. Guiry in Guiry, M.D. & Guiry, G.M. 20 August 2022. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway.; searched on 20 May 2024

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