Actinocyclus Ehrenberg, 1837

Lectotype species: Actinocyclus octonarius Ehrenberg

Original publication: Ehrenberg, C.G. (1837). Nachricht des Hrn Agassiz in Neuchatel über den ebenfalls aus mikroskopichen Kiesel-Organismen gebildeten Polirschiefer von Oran in Afrika. 1837: 59-61.

Type designated in: Boyer, C.S. (1927). Synopsis of North American Diatomaceae. Part I. Coscinodiscatae, Rhizosolenatae, Biddulphiatae, Fragilariatae. Proceedings of the Academy of Natural Sciences of Philadelphia 78(Suppl.): 1-228.

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Description: Cells barrel-shaped, probably mainly epiphytic on seaweeds but often encountered in nearshore plankton. Plastids numerous, discoid. Valves circular (rarely elliptical or triangular) with radial sectoring; valve face planar or concentrically waved. Surface corrugate with tiny external pores (too small to be seen by SEM) and a single marginal 'pseudonodulus'; sometimes with a distinct rim at the junction of face and mantle. Mantle often distinct with large, simple rimoportula openings. Some species with stepped mantles. Valve framework bullulate. Internally, areolae seen to be arranged in variously organised fascicles with domed closing vela and conspicuously expanded rimoportulae usually angled to the valve rim. Psedonodulus in a clear area. Copulae open. Valvocopula massive, fimbriate, underlapping a shelf projecting from the valve rim. Other copulae (2 or more) smaller.

The most recent alteration to this page was made on 2024-10-01 by G.M. Guiry.

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

Most recent taxonomic treatment adopted: Fourtanier, E. & Kociolek, J.P. (1999). Catalogue of the diatom genera. Diatom Research 14(1): 1-190.

Comments: Rattray (1890) was the first to discuss the genus in detail and the status of the pseudonodulus has been re-examined recently by Simonsen (1975). f shows a closing plate with an unperforate outer membrane and g the inside view suggesting this is the 'operculate' type of Simonsen. h on the other hand shows the inner view of Simonsen's 'areolate' form. Thin sections confirm that the pseudonodulus is not perforate. The function of the pseudonodulus is not known and there is clearly much still to be learnt about the range of structure. Simonsen uses it as a criterion to distinguish the family Hemidiscaceae (Actinocylus, Hemidiscus and Roperia). A freshwater species A. normanii has been recorded under various names during the last century (see Hasle, 1977) and caused much confusion. Hasle has shown clearly that it is truly an Actinocyclus. It is one of several basically marine algae which are becoming established in freshwaters, probably due to increasing eutrophication. Several recent publications have dealt with Actinocyclus species (e.g. Fryxell & Semina, 1981; Watkins & Fryxell, 1986). The bullulate wall is likely to prove typical of this genus and species without this feature may belong elsewhere (Andersen et al., 1980).

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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=43722

Citing AlgaeBase
Cite this record as:
G.M. Guiry in Guiry, M.D. & Guiry, G.M. 01 October 2024. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. https://www.algaebase.org; searched on 24 November 2024

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