[A concept of parasite species at the times of molecular studies]

The problem of species recognition in relation to parasite organisms is discussed, based on literature data. Taking into account that over 20 species concepts have hitherto been formulated, the choice of characters, which should define a species differs from author to author. Lately the differences in some gene fragments are regarded as one of most important feature for species differentiation. On this basis some lineages, genotypes or strains have been differentiated within some species, but in most cases the respective authors did not decide to elevate these units to the species level. The present paper focuses on the studies on species representing three genera (Taenia, Echinococcus, Trichinella) as they show, especially the complex studies on the species within the genus Trichinella, how big material is necessary to formulate any proper conclusion and, on the other hand, that the differences in the DNA sequences cannot be the only characters defining species; some other features (morphological, biological, behavioral) should not be considered redundant.