163,924 species and infraspecific names are in the database, 22,783 images, 63,106 bibliographic items, 484,278 distributional records.

Actinocyclus Ehrenberg, 1837

Empire Eukaryota
Kingdom Chromista
Phylum Bacillariophyta
Subphylum Coscinodiscophytina
Class Coscinodiscophyceae
Subclass Coscinodiscophycidae
Order Coscinodiscales
Family Hemidiscaceae

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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Taxonomic status: currently recognized as a distinct genus.

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

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 14 Aug 2017 by M.D. Guiry.

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).

Numbers of names and species: There are 354 species names in the database at present, as well as 73 infraspecific names. Of the species names, 103 have been flagged as accepted taxonomically on the basis of the listed literature under the species name. In some instances, opinions on taxonomic validity differ from author to author and users are encouraged to form their own opinion. AlgaeBase is a work in progress and should not be regarded as a definitive source only as a guide to the literature..

Names: ('C' indicates a name that is accepted taxonomically; 'S' a homotypic or heterotypic synonym; 'U' indicates a name of uncertain taxonomic status, but which has been subjected to some verification nomenclaturally; 'P' indicates a preliminary AlgaeBase entry that has not been subjected to any kind of verification. For more information on a species click on it to activate a link to the Species database):

Click here to also show infraspecific names in the list below.

Tomas, C.R., Eds (1996). Identifying marine diatoms and dinoflagellates. pp. 1-858. San Diego: Academic Press Inc.

Scott, F.J. & Thomas, D.P. (2005). Diatoms. In: Antarctic marine protists. (Scott, F.J. & Marchant, H.J. Eds), pp. 13-201. Canberra & Hobart: Australian Biological Resources Study; Australian Antarctic Division.

Verification of data
Users are responsible for verifying the accuracy of information before use, as noted on the website Content page.

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.

Created: 11 April 2002 by M.D. Guiry

Verified by: 14 August 2017 by M.D. Guiry

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M.D. Guiry in Guiry, M.D. & Guiry, G.M. 2021. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 27 October 2021.

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