Ethmodiscus Castracane, 1886

Lectotype species: Ethmodiscus punctiger Castracane

Currently accepted name for the type species: Ethmodiscus gazellae (C.Janisch ex Grunow) Hustedt

Original publication: Castracane, [C.A.] F. (1886). Report on the Diatomaceae collected by H.M.S. Challenger during the years 1873-76. In: Report on the Scientific Results of the Voyage of H.M.S. Challenger during the years 1873-76. Botany. Vol. II. (Murray, J. Eds), pp. [1]-178.

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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 drum-shaped with flat or domed valves. Free-living and the largest celled of any centric form, attaining 2-3 mm in diameter. Plastids not observed. A tropical marine planktonic genus, but whole cells rarely observed. Fragmented material forms large sedimentary deposits in tropical seas. Valves flat or domed, with a plain central area from which radiate rows of simple loculate areolae. These are interrupted by a plain ridge at the end of the valve face and then continue down the valve mantle in vertical rows. The areolae have inner and outer vela with fine pores. There is considerable variation in valve structure - some valves have rows of 'bottle-like' projections, some have no annulus, or marginal plain ridge. Relating these variants to cells which are also possibly heterovalvar (at least four slightly different valve types have been found) and usually fragmented, has proved difficult (see Round, 1980). Rimoportulae occur on both valve face and mantle. External slit-like openings of rimoportulae occur in a ring around the annulus or scattered in the centre. Other rimoportulae can be found around the edge of the valve face and, on the mantle near the valve margin, there are rimoportulae with small circular pores. Internally the central rimoportulae are sessile or slightly stalked and curved; those around the valve face edge are small, no larger than the areolae, those at the mantle edge are slightly larger and occur amongst the rows of areolae. Copulae split, areolate.

The most recent alteration to this page was made on 2022-06-17 by M.D. Guiry.

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

Gender: This genus name is currently treated as masculine.

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

Comments: This genus needs to be investigated by observation of whole cells, preferably from culture. It is an unusual genus in that three different kinds of rimoportulae occur on a single valve - a feature we have not noted in any other genus. Samples collected in nets are often fragmented owing to pressure on the fine bubble-like cells. Further studies are also required on its ecology. The genus has been confused with Coscinodiscus in early literature and also placed in a genus Antelminellia. It is clearly not close to Coscinodiscus and we separate it into its own order and family.

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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. 17 June 2022. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway.; searched on 15 June 2024

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