Tweet this page Like this page Email this page Share this page Home» Resources » Identification » Identification of algae » Freshwater algae » How to identify algae » Identification guide » Unicellular » Shallow groove encircles the cell equator Shallow groove encircles the cell equator Cell is covered by thick armoured plates; if horns are present, these are short and blunt (cf. Ceratium). Peridinium Thick armoured plates and horns are absent. Gymnodinium Cell is covered by thick armoured plates; long, sharp horns protrude from both ends of the cell. Ceratium