Molecular Identification and Phylogenetic Position of Chaunocephalus ferox (Digenea: Echinostomatidae) from the Asian Openbill (Anastomus oscitans) in Thailand

Chaunocephalus ferox (Rudolphi, 1795) is an intestinal trematode of the family Echinostomatidae that commonly infects waterbirds, including the Asian Openbill (Anastomus oscitans). Despite its wide geographic distribution and ecological relevance in migratory birds, molecular data for this species remain limited. This study aimed to characterize the genetic variation and phylogenetic position of C. ferox recovered from a deceased Asian Openbill in Thailand. Adult flukes were examined using nuclear (28S rDNA and 5.8S–ITS2) and mitochondrial (cytochrome c oxidase subunit 1; CO1) markers. Sequence analyses revealed low intraspecific variation among Thai isolates, with a single variable site detected in each marker. However, comparisons with sequences from Egypt, China, and Ukraine demonstrated measurable genetic divergence, suggesting possible geographic and host-associated structuring among C. ferox populations. Phylogenetic analyses based on nuclear and mitochondrial datasets consistently supported the monophyly of C. ferox within Echinostomatidae and confirmed its distinct genetic lineage among echinostomes. These findings provide baseline molecular data for a trematode parasite of migratory waterbirds, highlighting the potential role of avian hosts in the long-distance dispersal of helminths across wetland ecosystems. Broader geographic sampling is needed to better understand the population structure and evolutionary dynamics of this parasite.