Abstract
A moray eel [192.8 mm total length (TL)], collected in February 2025 from a mud and scattered rock slope at 1 m depth in the Yoshikawa Fishing Port, Konan City, central Kochi Prefecture, Japan, was identified as Gymnothorax taiwanensis Chen, Loh, and Shao, 2008, previously known only from Taiwan. The species differs from all congeners in having the following combination of characters: tail length 45.8%–48.7% of TL; total vertebrae 117–121; jaw teeth stout; vomerine teeth biserial; and iris orange. The present specimen extends the known distribution range of G. taiwanensis northward to Japan and represents the smallest recorded size of the species to date. Comparison with five additional specimens collected from Taiwan in January 2019 and July 2022, including a 707 mm TL individual that extends the known maximum size of the species, revealed coloration variations across body lengths. In addition, the study proposes including the flounced flap of the posterior nostril rim as a diagnostic character of G. taiwanensis, as it readily distinguishes this species from its congeners. The new standard Japanese name “Tankan-utsubo” is proposed for the species.