When we want to classify a group of organisms by the morphological features, dichotomous key can help.
Suppose we have 6 different organisms and we would like to classify them based on different morphological features.
First, the organism on the right does not have any leg(appendage). Thus, this organism can be classified out first.
The first organism being classified out is an earthworm, named Amynthas aspergillus (參狀遠盲蚓).
Second, the organism on the right have two pairs of wings, while the others do not.
The second organism is a cockroach, named Periplaneta americana (美洲家蠊) .
Next, the organism on the right do not have repeat segmented body.
The third organism is a spider, named Heteropoda venatoria(白額高腳蛛).
Then, the organism on the right only have one pair of legs per one segment while the others have two pairs of legs per one segment of body.
The forth organism is a centipede, named Rhysida immarginata(無棱衛蜈蚣).
Now we only have two organisms left. We can observe that the organism on the right has a node-shaped body segments while the left one does not.
The fifth organism is a millipede, named Helicorthorpha holstii (霍氏繞馬陸).
The last organism is also a millipede, named Trigoniulus corallinus (磚紅厚甲馬陸).
Finally, we can construct a dichotomous key according to the morphological features of different organisms.