Aulacodiscus Ehrenberg, 1844, nom. cons.

Holotype species: Aulacodiscus crux Ehrenberg

Original publication and holotype designation: Ehrenberg, C.G. (1844). Mittheilung über 2 neue Lager von Gebirgsmassen aus Infusorien als Meeres-Absatz in Nord-Amerika und eine Vergleichung derselben mit den organischen Kreide-Gebilden in Europa und Afrik. Bericht über die zur Bekanntmachung Geeigneten Verhandlungen der Königl. Preuss. Akademie Der Wissenschaften zu Berlin 1844: 57-97.

Description: Cells solitary, circular in valve view with conspicuous marginal processes. Truncated oblong in girdle view with the marginal processes protruding. Plastids not observed. A marine genus living associated with inshore sediments and sometimes attached to sand grains. Can form massive growths in the surf zone, e.g. along Copalis Beach, Oregon coast during certain years in the 1920s and 1930s (Lewin, 1974) and along California beaches recently (Holmes & Mahood, 1980). A very large, mainly fossil genus going back to the Cretaceous and exhibiting considerable diversity of valve and rimoportula form. Valve with a conspicuous hyaline area at the centre from which rows of loculate areolae radiate. The valve surface is often corrugated and the valve mantle is not differentiated from the rest of the valve. The areolae are closed by cribra externally and open internally by large foramina; we have some evidence that there is an internal occlusion of some kind in some species. Rimoportulae marginal, complex, opening externally either via a tube or onto a cap extending towards the valve centre. In capped forms, the processes often have 'fork-like' slits. The rimoportula is unique. The tube passes through the valve and ends internally in a curved slit, almost flush with the internal layer of the wall. This slit is either E-shaped or C-shaped and may be orientated with the opening of the E or C pointing to the centre or tangentially. Sometimes clear hyaline rays extend from the centre to the rimoportulae, these being best seen on the inside of valves. Copulae numerous, split, ligulate and antiligulate, fimbriate (at least on the valvocopula), with vertical rows of small areolae.

The most recent alteration to this page was made on 2017-01-27 by M.D. Guiry.

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

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: Reviewed by Rattray (1888a) and Ross & Sims (1970) and studied intensively by Burke & Woodward (1963-74). The structure of A. amherstia is discussed by Venkateswarlu & Round (1973) and by Sims & Holmes (1983) (who regard it as A. johnsonii var. amherstia) and A. Kittonii by Holmes & Mahood (1980). Both Holmes & Mahood and Ross & Sims (1970) consider that the morphology of the rimoportula is a useful specific taxonomic character.

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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. 27 January 2017. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway.; searched on 13 August 2022

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