Zoological Institute RAS, St. Petersburg, Russia (nema@zin.ru)
The goal of the taxonomic description is to be an adequate tool to identify the species precisely. A uniform species description standard within the genus gives the opportunity to construct a matrix of species characters for the genus, where the fields are defined by the description standard. The matrix may be easily converted to an electronic or a printed key. Characters of the description standard may be collected from the published retrieval systems (keys of experienced taxonomists) or their fragments (differential diagnoses, relationships).
The evident link between the species description standard and the corresponding matrix of species characters creates a problem for modern database approaches, namely whether the matrix should be one for the large group (order, family) or whether it is easier to construct the hierarchy of matrices (order>family; family>genus; genus>species). The hierarchy of matrices is more economic to input taxonomic data and to identify species. The important feature of the description standard is its long-term reliability and the flux of new species descriptions. This is especially important for the species of small genera. The principle of Vavilov’s homology series (the interspecies variability is similar in close genera) may be used and characters of the neighbouring large genera have to be included in the species description standard for the smaller genera, as well as detailed illustrations. Search of characters and the procedure of matrix creation are demonstrated on examples of species belonging to the nematode families Pratylenchidae, Parasitaphelenchidae, and Aphelenchoididae.