Zooplankton Identification and Taxonomic Keys
Goals of this practical
Gain familiarity with the diversity of zooplankton that is found in the Southern Ocean. Develop observational skills by producing and trialling taxonomic keys.
Gain experience with a high-level taxonomic key.
Background
How does one go about identifying the species, genus, etc., of a specimen whose identity is unknown (to the person who wishes to identify the speci-men)? The most useful tool for such identifications is the dichotomous key. A dichotomous taxonomic key contains information useful in identifying similar kinds of organisms, but is arranged in a way that allows the information to be used quickly.
A dichotomous key is a list of paired statements (each statement is called a lead) that guides you to the identification of a specimen. The paired leads (the pair of leads together is called a couplet) are contrasting descriptions of certain characteristics. In a good key, couplets are written so that you must choose one or the other of the leads as being true for your specimen. Couplet leads should always be mutually exclusive. Here is a bad couplet:
1 Many legs.
1' Few legs.
How many is "many"? How few is "few"? A better couplet would be:
1. Two legs or more.
1' No legs.
This couplet allows no ambiguity. The leads are mutually exclusive. In addi-tion, the leads in a couplet should be parallel; that is, both should ask questions about the same character(s).
To use a dichotomous key, one begins with the first couplet, deciding which statement is true for a specimen. The key may then tell you what taxon you have, or it may direct you to another couplet. Follow the key until you have arrived at a name.
Here's an example of a key to some kinds of fruit.