Taxonomy and systematics

Résumé 0

Taxonomy is the science of naming and describing organisms. It is a highly formalized science whose rules are established and revised regularly by an International Commission of Zoological Nomenclature created in 1895. The International Code of Zoological Nomenclature contains all the rules for designating animal species which are the same for all zoological groups.One of its basic principles is that the first name given to a species has priority over the others. It is not uncommon for taxonomic revisions of a group to reveal that some species had been described under different names, because the authors did not have access to all available information or had made an error. In these conditions, the so-called priority rule must be applied. This sometimes leads to a change in the name used for the species up to that time. The situation may prove even more complex, as illustrated by the case of Schilbe mystus (see box “Who is Schilbe mystus?”).Another well-known case of ambiguity is that of the mounted holotype of Synodontis xiphias described in 1864 by Günther, which has a long and pointed snout similar to a swordfish. The species had never been recorded since then, for a perfectly good reason: an x-ray showed that the long snout was a fake nose, resulting from a metal frame used in mounting the animal (Poll, 1971) (figure 8.1). The holotype of Synodontis labeo Günther, 1865, described later, belongs to the same species, but the name S. xiphias remains valid in application of the principle of priority, and despite the deformity of the specimen retained as the type.Systematics is the study of the diversity of organisms and the relationships between these organisms. Its goal is to classify species and detect phylogenies – a purpose that differs from the objectives of taxonomy. Classification consists of recognizing and defining groups or taxa (that is, a set of organisms that share a specific character) that taxonomists will then have to name. According to the hierarchical classification proposed by Linnaeus (1758), each level of the hierarchy corresponds to a taxon name. While ideas governing classification in particular have evolved significantly since the 18th century, the basic rules stated by Linnaeus remain solid. The discipline currently known as biosystematics is a modern approach to taxonomy and phylogeny that makes use of information from different sources: morphology, genetics, biology, parasite specificity, behaviour, and ecology. This type of approach is undoubtedly set to develop further.