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Name derivation:

From the Greek keration, small horn or spike (as on a unicorn)


Ceratium tetraceros  Schrank  1793; There are 296 species of which 81 have been accepted taxonomically (Guiry and Guiry 2013)

Order Gonyaulacales;  Family Ceratiaceae



Biflagellate unicells with extended arms.  Freshwater species have an elongate anterior arm and two or three somewhat shorter posterior arms (‘horns’).  Marine species vary from nearly linear with one anterior and one posterior arm, to anchor-shaped with two anterior and one posterior arm.

Cells of some species are armored with relatively thick plates of cellulose, and extends out into the elongate 'horns'. A lateral wrap-around groove (' cingulum') is evident and can be either equatorial or displaced toward one end of the cell. A second groove ('sulcus') is perpendicular to the cingulum lying on the cell surface.

Both flagella emerge from the junction of the cingulum and sulcus, one projecting backward along the sulcus that pushes the cell, the other wrapped around the cell within the cingulum enabling rotatory movement of the cell.

Numerous discoid chloroplasts are located throughout the cell.  A large nucleus is centrally located.

Cell division occurs in motile cells.  One daughter cell inherits the epitheca, and regenerates a new hypotheca, and the reverse happens with the other daughter cell.  This is similar to diatom cell regeneration, but the two daughter cells have different morphology (as they do in monoraphe diatoms).

Ceratium cells are photosynthetic but also contain vacuoles that suggest phagotrophy.

Aplanospores (no flagella) are common, often after blooms. C. hirundinella has angular spores that are uninucleate, thick walled, and packed with glycogen as a storage reserve.  As most spores they are resistant to dessication and remain viable for years.  When they germinate they form a zoospore (flagellated) that starts as a spherical cell (similar to Gymnodinium) that develops within hours into the typical horned cell.


Similar genera:




Most are planktonic in marine or brackish water. A few occur in freshwater, such as C. hirundinella, an indicator of hard waters.  C. carolinianumis found in bogs.

Ceratium along with Peridinium is a common bloom forming dinoflagellate in freshwater lakes, and proliferate in relatively nutrient-poor but organically rich habitats.


Although marine species of Ceratium are often associated with ‘red tides’ there does not appear to be evidence that they produce secondary metabolites toxic to fish or mammals.


Graham, L. and L. Wilcox  2000. Algae. Prentice-Hall

Guiry, M.D. and G.M. Guiry  2013.  AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 15 September 2013. Patterson, D.J.  1996.  Free-Living Freshwater Protozoa. John Wiley & Sons, Inc.

Smith, G.M.  1950.  The Freshwater Algae of the United States.

Schrank, F. von Paula  1793.  Mikroskopische Wahrnehmungen.  Der Naturforscher (Halle) 27: 26-37.





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