DICHOTOMOUS KEY TO COMMON PROTISTA
Instructions: When using a dichotomous key to identify an organism always start at “1”. Read the two statements given and choose the one which best describes the organism you are looking at. To the right of the correct statement you will either find the identification of your organism OR directions to “go to” another set of statements in the key. Jump to the new set of statements, if instructed to do so, and again choose the one which best describes your organisms. Continue, in this way, until you have identified your organism.
1. Protist is colorless (may appear clear, white, or gray)…………………………………………………Go to 2
Protist has color (may appear green, brown-ish, or pink-ish)………………………………………Go to 9
2. Protist slowly oozes along, has no cilia or flagella, and has no definite shape……………….Amoeba
Protist moves using cilia or flagella and has a definite shape………………………………………Go to 3
3. Protist seems to have many short, hair-like cilia around the entire cell or clumped
in specific areas………………………………………………………………………………………………………Go to 4
Protist seems to be missing cilia but has one to eight long, thin flagella (the flagella
are usually hard to see they are so thin)……………………………………………………………………Go to 8
4. Protist has beating cilia that seem to cover the entire cell like short, little hairs…………….Go to 5
Protist has beating cilia, but they are clumped in certain areas and do not cover
the entire cell…………………………………………………………………………………………………………Go to 7
5. The protist is large, very long and skinny—almost like a thin worm……………………………..Spirostomum
The protist is more oval-shaped and not so long………………………………………………………..Go to 6
6. The protist is elongated, fairly large, and glides through the water—often backing
up and then swimming forward again……………………………………………………………………….Paramecium
The protist is oval-shaped, small, and often swims through the water in a
spiral motion………………………………………………………………………………………………………….Colpidium
7. The protist has groups of cilia that look like spikes or spines sticking out.
The protozoan is medium in size and tick-shaped………………………………………………………Euplotes
The protist looks like a small vase that is attached to a stalk. Cilia are located
around the top of the “vase”. Because the protozoa is attached to a stalk it
can’t swim around, however, the stalk can rapidly contract like a spring to pull
the protozoa away from danger. The protozoan is medium in size………………………………Vorticella
8. Protist is very small, shaped like a teardrop, and has 8 flagella to help it move around….Giardia
Protist is very small, shaped like a teardrop, and has 1 flagella to help it move. It is
flattened and has a round feeding structure at one end……………………………………………..Centropyxis
9. Protist is green colored (an algae)……………………………………………………………………………Go to 10
Protozoa is brown-ish or pink-ish………………………………………………………………………………Go to 13
10. The green colored protist is a single cell……………………………………………………………………Go to 11
The green colored protist is a group of cells………………………………………………………………Go to 12
11. Protist is an algae. The algae is small and elongate (slipper-like) with a flagella
used for locomotion………………………………………………………………………………………………..Euglena
Protist is an algae. This algae is small and oval shaped with green spheres inside
and spins/bounces in water in lazy circles…………………………………………………………………Cyanophora
12. Protist is an algae. This algae is actually a colony of many green cells forming a
sphere which spins through the water………………………………………………………………………Pandorina
13. Protist is a pink-ish colored, large, covered with cilia, and slowly glides through
the water……………………………………………………………………………………………………………….Blepharisma
Protist is brown-ish colored, large, spore-like ball. It is stationary and has stalks
Attached………………………………………………………………………………………………………………..Diffulgia