Amphitetras Ehrenberg, 1840

Holotype species: Amphitetras antediluviana Ehrenberg

Original publication: Ehrenberg, C.G. (1840). Über noch zahlreich jetzt lebende Thierarten der Kreidebildung und den Organismus der Polythalamien Preprint of Abhandlung der Könglichen Akademie der Wissenschaften zu Berlin aus dem Jahre 1839 [1841] with different pagination. pp. 1-94, 4 pls. Berlin.

Type designated in: 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.

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Description: Cells forming zig-zag colonies attached to seaweeds, often with conspicuous mucilage pads between cells; these pads appear 'collar-like' in some of our material. Plastids numerous, plate-like. Not uncommon and probably of world-wide distribution. Valves quadrate, often with concave sides. Superimposed upon the quadrate morphology there is a central circular dome with a depressed centre. Prominent ocelli occur on low elevations at the angles. Valve framework massive, sometimes granulose or spinulose, and sometimes with branching spinules near the mantle edge. Areolae occluded by cribra located near the outside surface, some of which bear fine spinules. The edge of the valve mantle is formed into internal and external flanges; the latter is turned upwards parallel to the valve mantle and is often quite deep and in some valves finely granular. Internally the underlying centric radiating system of costae is obvious at the centre of the valve; here there are a few simple pores through the framework. Rimoportulae absent. Copulae are complete, areolate with cribra of the same form as those of the valve but lying flush with the siliceous framework which is more laminate than that of the valve. The valvocopula has an inwardly directed pars interior, which underlaps the valve.

The most recent alteration to this page was made on 2019-01-10 by M.D. Guiry.

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

Most recent taxonomic treatment adopted: Sims, P.A., Williams, D.M. & Ashworth, M.[P.] (2018). Examination of type specimens for the genera Odontella and Zygoceros (Bacillariophyceae) with evidence for the new family Odontellaceae and a description of three new genera. Phytotaxa 382(1): 1-56, 156 figs, 2 text-figs.

Comments: The siliceous framework of the valve is very similar to that of Isthmia. The genus Amphitetras has formerly been placed in Biddulphia, Triceratium and Stictodiscus. With the redefinition of these genera, Amphitetras remains as a distict entity. An extremely detailed and fascinating account of A. antediluvianum is given by Liebisch (1928) in which he also figures auxospore formation involving expansion of the cytoplasm in the distal region of the hypocingulum which then splits as further expansion of the auxospore wall occurs. The primary cell is formed within the auxospore while still attached to the hypovalve, as in Melosira varians. The classification of genera in the order Biddulphiales is still in a state of flux. Amphipentas is possibly to be included within Amphitetras but a position in Stictodiscus also needs consideration.

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Contributors
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.

Linking to this page: https://www.algaebase.org/search/genus/detail/?genus_id=44350

Citing AlgaeBase
Cite this record as:
M.D. Guiry in Guiry, M.D. & Guiry, G.M. 10 January 2019. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. https://www.algaebase.org; searched on 22 November 2024

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