Lithodesmium Ehrenberg, 1839

Holotype species: Lithodesmium undulatum Ehrenberg

Original publication and holotype designation: Ehrenberg [C.G.] (1839). Über jetzt wirklich noch zahlreich lebende Thier-Arten der Kreideformation der Erde. Bericht über die zur Bekanntmachung geeigneten Verhandlungen der Königl. Preuß. Akademie der Wissenschaften zu Berlin 1839: 152-159.

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Description: Cells rectangular in girdle view and joined to form filaments. Plastids numerous, discoid. A marine planktonic genus of few species, only the type being frequently recorded. Valve triangular (sometimes quadrangular), with a central tubular spine and a marginal ridge; an elevation at each angle; a fold or undulation across the angles, which creates a more-or-less circular, 'centric' middle part on which the triangular shape seems superimposed. Uniserate rows of areolae radiate from the centre. The marginal ridge is high and extends upwards from the edge of the valve face, even around the elevations; it continues the line of the mantle. It has previously been known as the 'lamella' (Verbindungslamelle of Hustedt. 1930) and has pores that are much larger than the areolae on the valve itself; they are probably unoccluded. The marginal ridges of sibling valves overlap. At the angles of the valves, the ridge is lower and leaves a large hole opening into the intercellular space. At this point the ridge of one valve appears to change from overlapping to underlapping. Hustedt (1930) carefully pointed out that the cells were connected by the marginal ridge and that these had nothing to do with the girdle bands. The central long tube forms the external opening of the rimoportula which internally has two slits in line (Hasle, 1975, fig. 1496) and has been termed a bilabiate process (von Stosch, 1977). The cingulum is composed of segments arranged in four rows. Each row consists of three or more segmants (depending upon the number of sides to the valve), which are areolate and ligulate (see also von Stosch, 1980a).

The most recent alteration to this page was made on 2020-01-31 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 neuter.

Most recent taxonomic treatment adopted: Round, F.E., Crawford, R.M. & Mann, D.G. (1990). The diatoms biology and morphology of the genera. pp. [i-ix], 1-747. Cambridge: Cambridge University Press.

Comments: The structure of this genus and of Ditylum have many features in common and the early light microscopists were correct in grouping the two together. Von Stosch (1980a) emphasises the difference between the lamellate marginal ridge of Lithodesmium and the row of double spines in Ditylum. Apart from overall shape neither genus has much in common with the Triceratium group, which is in a confused taxonomic state. They are often allied with Triceratium itself, but we do not accept a close relationship.

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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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M.D. Guiry in Guiry, M.D. & Guiry, G.M. 31 January 2020. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway.; searched on 03 March 2024

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