First record of Paradilepis scolecina (Rudolphi, 1819) Hsü, 1935 (Cestoda: Gryporhynchidae) in Republic of Korea with notes on ultrastructure and ecological risk in great cormorants, Phalacrocorax carbo sinensis (Staunton, 1796) (Aves: Phalacrocoracidae)

Paradilepis scolecina (Rudolphi, 1819) Hsü, 1935 is a tapeworm widely distributed across the globe that uses piscivorous birds as definitive hosts. Although various piscivorous birds inhabit the Republic of Korea (Korea), this species has not previously been documented in the country. In this study, we report its occurrence in resident great cormorants, Phalacrocorax carbo sinensis (Staunton, 1796), based on integrated morphological, molecular, and ultrastructural analyses. The recovered specimens exhibited 20 rostellar hooks of parvoid type arranged in a double row consistent with the scolecina pattern, allowing distinction from other congeners. Partial LSU sequences of the specimens in this study showed the highest identity to P. scolecina isolates from South Africa and Lithuania (GenBank accession no. MH062156 & PQ570010, 100% identity), while SSU sequences were closest to Paradilepis sp. references (MH699816, 98.1%). Combined BLAST and phylogenetic analyses supported their identification as P. scolecina. Notably, scanning electron microscopy revealed a previously undescribed cirrus surface featuring rose-thorn-shaped spines interspersed with capilliform filitriches-representing the first such ultrastructural description within the family Gryporhynchidae. The shift of Ph. c. sinensis increasing tendency toward year-round residency in Korea may enhance parasite transmission by increasing contact with local freshwater hosts, a hypothesis that warrants further ecological investigation. Additionally, the presence of P. scolecina may have implications for wild fish populations and nearby aquaculture facilities, particularly if intermediate or paratenic hosts include economically important species. These findings contribute to the growing knowledge of the parasite fauna of cormorants in Korea and underscore the need for further research into the transmission dynamics and host range of trophically transmitted cestodes in East Asian freshwater ecosystems.