In this article, nucleotides belonging to the ITS region of the ribosomal DNA of Glanitaenia osculata (Goeze, 1782) found in the flounder (Silurus glanis. Linnaeus, 1758) were analyzed and the phylogenetic relationships of this species were studied. Glanitaenia was differentiated from the other genera of the subfamily Proteocephalinae by the possession of a well-developed, functional apical sucker with a deep cavity (the apical sucker in different species of the Proteocephalus-aggregate is vestigial, without any cavity, or completely absent – see Scholz et al., 1998). However, some morphological details, including characteristics that are recently considered to be of potential taxonomic and phylogenetic importance, such as the development of the uterus, the relative size of the ovary, the morphology of the eggs and terminal genitalia (the distal part of the vaginal canal), and the course of osmoregulatory canals were not provided.