1. How does it move? It swims with one or two long whips, often green; or it is a rolling green ball
2. Alone or in a colony? A single cell

Which single flagellate?

Look for the colour, an eyespot, and whether the cell changes shape.

1. Green, elongated, red eyespot; squirms and changes shape when it stops→ Euglena
2. Green, flat and leaf-shaped with a tail spine; rigid and twisting→ Phacus
3. Green, tiny, round to oval with two equal flagella→ Chlamydomonas
4. Colourless, gliding with one thick flagellum held straight ahead→ Peranema
5. Golden-brown, armoured, spinning; a groove around the middle or long horns→ Dinoflagellates
6. A round brown or orange shell with a flagellum poking out of a collar→ Trachelomonas

Not sure? How to judge size by the field of view · This step looks wrong