Results of study of Leptomonas nabiculae using various molecular markers and different material (cultures D2 et Nfm2) contradicted each other and taxonomic position of this species. We investigated morphology of the cells in these cultures as well as in hapantotype of L. nabiculae and those of L. peterhoffi and L. occidentalis that had been described from the same host species. We also reconstructed 18S rRNA gene phylogeny using sequences from both cultures. The D2 culture according to its morphology and phylogenetic position revealed to be a Crithidia that had accompanied L. nabiculae in a mixed infection. We named it Crithidia dedva. The cells in the hapantotypes of the three Leptomonas species and those of the Nfm2 culture represent a single species that is a Herpetomonas (H. nabiculae) judging by morphology and molecular phylogeny. We also showed that the sequence of 18S rRNA gene that had been formerly determined represents a chimaera. This had resulted in the wrong position of this species on the phylogenetic tree that had contradicted results of the analysis of 5s rRNA gene.