Back from the dead: validity and taxonomic position of Cotylurus brandivitellatus (Belogurov, Maksimova et Tolkacheva, 1966) in light of the integrative taxonomy approach.

Accurate species identification is essential for biodiversity research, especially in the field of parasitological systematics. In particular, the incorporation of DNA-based methods in the study of Digenea has transformed taxonomy by allowing for precise species delimitation, clarification of life cycles, and the identification of cryptic diversity. However, to prevent taxonomic misidentification, a growing concern in public sequence databases, these molecular techniques must be supplemented with high-quality morphological data. This study provides an integrative assessment (combining both morphological and molecular data) of Cotylurus brandivitellatus, based on adult specimens obtained from naturally infected mute swan (Cygnus olor) in Gdańsk Pomerania. The observed morphological characteristics are consistent with the original description of C. brandivitellatus and align with the established description of the genus Cotylurus. Phylogenetic analysis, utilizing concatenated LSU rDNA and COI mtDNA markers, confirms the distinct taxonomic status of C. brandivitellatus. It forms a sister clade with C. strigeoides, which is clearly separate from other species within the Cotylurus genus. These findings validate the existence of C. brandivitellatus and offer new insights into species delineation and evolutionary relationships within Cotylurus, highlighting the importance of integrative approaches in trematode systematics.