Figure 2-1. Pictorial key to common classes and orders of adult arthropods of public
health importance.
c. Another type of key is known as the couplet key, illustrated in figure 2-2,
"Standard Identification Key to Common Classes and Orders of Arthropods of Public
Health Importance." It has pairs of descriptive statements against which you match the
specimen you want to identify. In each pair, only one statement fits your specimen. You
select the statement that describes your specimen and then look at the number in the
right hand column. This number wiII direct you to the number of another pair of
statements (not a page number) that may or may not be the next number in sequence.
When you have developed enough information to permit identification, the statement
wiII be followed by the name of the specimen. You have now determined what your
specimen is. Remember that not all keys identify to genus or species levels. For
example, the couplet key shown as figure 2-2 wiII identify class and order and
sometimes famiIiar and common names for each. The couplet key is more Iikely to be
used in basic reference works and in scientific papers. Its advantage Iies in its relative
completeness and its capacity for giving very detailed information in a systematic
manner. For purposes of rapid identification in the field, the pictorial key is more useful
MD0170
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