All sorts of organisms live in Lake Michigan. Although Russell Cuhel is familiar with many of the ecosystem’s species, he sometimes encounters unfamiliar forms of life. That is when he uses a species identification tool called a key.
A key uses a set of statements or questions to guide you through the identification process. Most keys are dichotomous keys, meaning that each step uses two contrasting options. From the two choices, you select the one that best describes your specimen. Then you are guided through additional statement pairs until you eventually identify the species. Here is a sample that shows how a key can be used to identify three types of mussels:
| 1a The mussel has a bluish black shell |
common or blue mussel |
| 1b The mussel has a patterned shell |
go to 2 |
| 2a Shell halves are symmetrical, shell triangular in shape |
zebra mussel |
| 2b Shell halves are asymmetrical, shell rounder in shape |
quagga mussel |