First record of Corynosoma sp. (Acanthocephala: Polymorphidae) recovered from a northern fur seal, Callorhinus ursinus (Chordata: Otariidae), in Korea.

Importance: Species of the genus Corynosoma are acanthocephalan parasites widely distributed among fish-eating mammals and birds. However, their occurrence in pinnipeds within Korean waters has been rarely documented. Previously, only a single case involving C. strumosum in a spotted seal has been reported. Clarifying the presence and distribution of Corynosoma in Korean waters is essential for improving regional parasite surveillance and assessing related ecological and zoonotic risks.

Objective: The northern fur seal (Callorhinus ursinus) inhabits the North Pacific and occasionally reaches Korean waters during its nonbreeding season. Despite this migratory presence, no acanthocephalan infections have been reported in this host in Korea. This study sought to fill that gap by examining a bycaught northern fur seal for intestinal parasites and characterizing the recovered acanthocephalans.

Methods: In 2013, a dead northern fur seal was recovered off Goseong-gun, East Sea, Korea. Acanthocephalans collected from the small intestine were examined using light microscopy, histology, and scanning electron microscopy. Morphological features were compared with existing descriptions.

Results: Twenty-two specimens (3 males, 19 females) were identified as Corynosoma spp., exhibiting sexual dimorphism and typical proboscis hook arrangements (16-20 rows, 8-11 hooks/row). Genital spines were present only in males. Morphological similarities with C. strumosum, C. simile, and C. magdaleni were noted, but species-level identification was inconclusive due to overlapping traits and lack of genetic data.

Conclusions and relevance: This first report of Corynosoma from a northern fur seal in Korea expands the known host and geographic range of the genus. The findings highlight the need for further morphological and molecular studies to better understand parasite diversity and potential zoonotic risks in Korean marine ecosystems.