Cladistic analysis and a comparison between taxonomical criteria in the classification of nematodes

Abstract

Nematodes are characterized by an exceedingly high degree of structural homogeneity, their species having adopted the most various conditions of life without undergoing conspicuous morphological changes. For this reason, the systematic study of the phylum is particularly difficult and the classification of nematodes is still in a state of great instability. The present classification of nematodes has been almost entirely constructed with the traditional taxonomical criteria of the evolutionary school, based on the overall similarities of the species rather than on their phylogenetic relationship. Only recently have some taxonomists begun to study selected taxa of nematodes on phylogenetic bases, using the cladistic analysis of Hennig. In order to compare the different criteria and their effects on the classification of nematodes, a taxonomical study recently conducted by the present author on the superfamily Ac-tinolaimoidea is discussed and analyzed. © 1991 Taylor & Francis Group, LLC.