Dinoflagellates - Ceratium in fresh water
Ceratium belongs to the major group of Dinoflagellates. It is common in the plankton in lakes, but find their greatest diversity in the sea.
The most typical specie from fresh water is Ceratium hirundinella with three rod-like portions, which commonly are called horns. The longest horn is an extension of the anterior end of the cell.
Cyst of Ceratium hirundinella. The cyst appears in late summer or early autumn. They sink to the bottom and remain there until next spring. When the water begins to warm up they germinate. The size is about 45-90 my.
Image of Ceratium hirundinella taken with an electron-microscope. The cell is divided into two halves by a groove. Each groove contains a flagellum. The cell wall is composed of plates and the pores provide water supply.
Ceratium carolinianum.