The Ordovician acritarch genera Tranvikium and Ampullula: their relationship and taxonomy

A restudy of the Ordovician (Arenig–Llanvirn) acritarch taxa Tranvikium polygonale Tynni, 1982, and Ampullula suetica Righi, 1991, indicates that they represent extremes in a single morphological plexus. At one extreme are forms with a polar ‘excystment’ aperture (closed by an operculum or two operc...

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Bibliographic Details
Published in:Review of palaeobotany and palynology 2000-10, Vol.112 (1), p.23-38
Main Authors: Uutela, Anneli, Sarjeant, William A.S.
Format: Article
Language:English
Subjects:
acritarchs
Ampullula
Chlorophyceae
Finland
Ordovician
Sweden
Tranvikium
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Summary:A restudy of the Ordovician (Arenig–Llanvirn) acritarch taxa Tranvikium polygonale Tynni, 1982, and Ampullula suetica Righi, 1991, indicates that they represent extremes in a single morphological plexus. At one extreme are forms with a polar ‘excystment’ aperture (closed by an operculum or two opercular pieces) and a smaller opening (plugged or open) at the opposite pole; at the other are forms lacking a polar aperture but having, at the opposite pole, a tube open distally and plugged or open basally. New morphological terms for these structures are proposed. The genera and species are treated as synonyms and an emended diagnosis is given for Tranvikium polygonale, incorporating this whole morphological plexus. The possible purposes of the structures exhibited and the likely affinity of T. polygonale to various groups of algae are discussed. The emendation of Ampullula by Brocke (1997) is rejected and the genus Stelomorpha Yin, 1994 retained, with an emended diagnosis. The new combination Stelomorpha princeps ( Brocke, 1997) Uutela and Sarjeant is proposed.
ISSN:0034-6667
1879-0615
DOI:10.1016/S0034-6667(00)00033-6