Dichotomous Key for Protozoa
Start at number 1, comparing the observed protozoan to each of the characteristics stated per
number in the key. Proceed according to the key until it terminates in the name of the protozoan.
Characteristic Go to Number
1. White or colorless 2
Colored 8
2. Creeping (sliding) slowly or floating without
apparent motion
3
Exhibits other motion 7
3. Spherically shaped with radiating “spines” Actinosphaerium
Not spherical in shape 4
4. Shape remains constant 5
Shape changes 6
5. Possesses flattened test or shell without
embedded or attached material; pale to brown
in color
Arcella
Possesses dome-shaped test or shell with
attached particles, usually of sand
Difflugia
6. Small; creeps using pseudopodia (false feet);
single disc-shaped nucleus
Amoeba
Large; creeps using pseudopodia; many(100’s) of
small nuclei
Pelomyxa
7. Cell has hair like structures (cilia) 16
Cell’s organ of locomotion is long whip-like
flagella (no cilia)
9
8. Green color 9
Color not green 23
9. Colony of many cells 11
Single, motile cells 10
10. One observed locomotor flagella 15
Two observed locomotor flagella 14
11. Colony flat, disc-shaped, usually containing
sixteen cells
Gonium
Colony spherical in shape 12
12. Colony contains 32 cells or less 13
Colony contains more than 32 cells Volvox
13. Colony 32 cells Eudorina
Colony contains sixteen cells Pandorina
14. Cells elongated with narrowed posterior Chilomonas
Cell oval-shaped Chlamydomonas
15. Cell elongated, green in color Euglena
Cell elongated, colorless , with a broad, rounded
or truncate posterior during locomotion; highly
plastic when stationary, often appears to vibrate