BEGINNER'S ORIENTATION

Identification of plants and animals in biology is frequently aided by using a dichotomous key, a device constructed from a series of highly organized couplets. A couplet consists of (usually) two descriptions which should represent mutually exclusive choices (often it is a particular combination of characteristics that determines the difference). Both choices are read and compared with the specimen to be identified. The term specimen is used to indicate the item under examination. Having several individuals of the same species or item to observe is often helpful. Once a decision is made, that selection directs you to another couplet (either the next in order or one further on), and this process is repeated until a conclusion (successful identification) is reached. At this point a verification step is important: compare the specimen with any details in the description and/or any available figures. Also consider habitat and location where the collection was made. If the description seems satisfactory, a correct identification probably has been achieved. If the description is not satisfactory in one or more important particulars, back up (the keys are constructed to accommodate this) to some earlier couplet and start over, questioning each decision more carefully. A helpful discussion on using and making dichotomous keys may be found in the article A Few Words About KEYS by Gordon Ramel, adapted from Harold Oldroyd (1958).

Here is an example of a couplet in a dichotomous key (this is the first couplet in Keys to Aquatic Biota of the Hawaiian Islands) :

Note that the description under "1b" could fit some animals like sponges, which do not appear to be capable of movement. This fact will be taken into consideration in the key, and the choice here will not lead directly to plants only. Indeed, we are expanding the keys to include physical (geological) features and specimens to enhance an ecological approach to aquatic biology. Choice "1b" fits as well for a rock. Proceeding further (to the next couplet in the key) is accomplished by clicking on the number following the description that suits the specimen being identified.

It is not unusual to reach a wrong conclusion when using a dichotomous key. Choices must be made all along the way that are not always as clear cut as we would hope them to be. Problems of this sort reflect both the skill and experience of the author of the key AND variability that is inherent in every species population. Also coming into play are subtleties that arise when one attempts to differentiate between two species using just a few characteristics (try yourself to differentiate between cats and dogs using just a few sentences). In some cases, you may find that neither choice fits very well, or you may not always understand exactly what is being discussed. It is helpful to write down couplet numbers where there is uncertainty and return to these questionable decisions if the end result is not satisfactory. Because mistakes in interpretation along the way are common, it is important not to accept the answer the key leads you to without then comparing the specimen carefully with final descriptions and/or pictures. There is no easy way to weigh the importance of each decision made at a couplet, and once a mistake is made, proceeding on to a wrong answer can be surprisingly easy (and obvious only if the verification step is followed). An additional problem occurs when the species you have is not even in the key. In this case, it is very likely not to fit either of the choices at some point in the process because the couplets were developed with certain species in mind. Note that you can go backwards in the key by clicking on the number in parentheses at the start of the first description in each couplet, but be careful where a couplet serves as the destination for more than one preceding couplet.

We have tried to mix standard English terminology with specialized terms (the latter often presented initially in parentheses). Any word that appears in bold is defined to some extent at that point in the key and is thus made to stand out in case you encounter the term elsewhere and want to clarify its meaning. Perhaps a glossary can be added some day. Although the keys now have minimal figures, the use of drawings in particular to clarify choices is considered highly desirable, and drawings will be added as the keys are improved over time. Photographs of the organisms treated in the key are being added as these are acquired. In some cases, sources of pictures on the WWW will be listed in our CPIE Hawai`i Aquatic Biota Listing